Doc fix.

[gsasl.git] / doc / gsasl.texi

\input texinfo   @c -*- mode: texinfo; coding: us-ascii; -*-
@c This file is part of GNU SASL.
@c See below for copyright and license.

@setfilename gsasl.info
@include version.texi
@settitle GNU Simple Authentication and Security Layer @value{VERSION}
@finalout

@c Unify some of the indices.
@syncodeindex tp fn
@syncodeindex pg fn

@copying
This manual is last updated @value{UPDATED} for version
@value{VERSION} of GNU SASL.

Copyright @copyright{} 2002, 2003, 2004, 2005, 2006 Simon Josefsson.

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
copy of the license is included in the section entitled ``GNU Free
Documentation License''.
@end quotation
@end copying

@dircategory GNU Libraries
@direntry
* libgsasl: (gsasl).    Simple Authentication and Security Layer Library.
@end direntry

@dircategory GNU utilities
@direntry
* gsasl: (gsasl)Invoking gsasl.         Command line interface to GNU SASL.
@end direntry

@titlepage
@title GNU SASL
@subtitle Simple Authentication and Security Layer for the GNU system
@subtitle for version @value{VERSION}, @value{UPDATED}
@author Simon Josefsson
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@ifnottex
@node Top
@top GNU Simple Authentication and Security Layer
@insertcopying
@end ifnottex

@menu
* Introduction::                How to use this manual.
* Preparation::                 What you should do before using the library.
* Using the Library::           High level overview of how to use the library.
* Properties::                  How to specify username, password, etc.
* Mechanisms::                  Mechanism specific information.
* Global Functions::            Functions that can be used at all times.
* Callback Functions::          Set and use callbacks.
* Property Functions::          Specify username, password etc.
* Session Functions::           Perform an authentication.
* Utilities::                   Functions for various odd things.
* Error Handling::              Error codes and such.
* Examples::                    Demonstrate how to use the library.
* Acknowledgements::            Whom to blame.

* Invoking gsasl::              Command line interface to the library.

Appendices

* Protocol Clarifications::     Our notes on the SASL protocol.
* Old Functions::               Descriptions of old API functions.
* Copying This Manual::         How you can copy and share this manual.

Indices

* Concept Index::               Index of concepts and programs.
* Function and Data Index::     Index of functions, variables and data types.
@end menu

@c **********************************************************
@c *******************  Introduction  ***********************
@c **********************************************************
@node Introduction
@chapter Introduction

GNU SASL is an implementation of the Simple Authentication and
Security Layer framework and a few common SASL mechanisms.
@acronym{SASL} is used by network servers (e.g., @acronym{IMAP},
@acronym{SMTP}) to request authentication from clients, and in clients
to authenticate against servers.

GNU SASL consists of a library (`libgsasl'), a command line utility
(`gsasl') to access the library from the shell, and a manual.  The
library includes support for the framework (with authentication
functions and application data privacy and integrity functions) and at
least partial support for the CRAM-MD5, EXTERNAL, GSSAPI, ANONYMOUS,
PLAIN, SECURID, DIGEST-MD5, LOGIN, and NTLM mechanisms.

The library is easily ported because it does not do network
communication by itself, but rather leaves it up to the calling
application.  The library is flexible with regards to the
authorization infrastructure used, as it utilize a callback into the
application to decide whether a user is authorized or not.

GNU SASL is developed for the GNU/Linux system, but runs on over 20
platforms including most major Unix platforms and Windows, and many
kind of devices including iPAQ handhelds and S/390 mainframes.

GNU SASL is written in pure ANSI C89 to be portable to embedded and
otherwise limited platforms.  The entire library, with full support
for ANONYMOUS, EXTERNAL, PLAIN, LOGIN and CRAM-MD5, and the front-end
that support client and server mode, and the IMAP and SMTP protocols,
fits in under 60kb on an Intel x86 platform, without any modifications
to the code.  (This figure was accurate as of version 0.0.13.)

The library is licensed under the GNU Lesser General Public License,
and the command-line interface, self-tests and examples are licensed
under the GNU General Public License.

@float Illustration,fig:abstraction
@image{abstraction,10cm,5cm}

@caption{Logical overview showing how applications use authentication
mechanisms through an abstract interface.}

@end float

@menu
* Getting Started::
* Features::
* SASL Overview::
* Requirements::
* Supported Platforms::
* Getting help::
* Commercial Support::
* Downloading and Installing::
* Bug Reports::
* Contributing::
@end menu

@node Getting Started
@section Getting Started

This manual documents the GNU SASL Library programming interface.  All
functions and data types provided by the library are explained.

The reader is assumed to possess basic familiarity with SASL and
network programming in C or C++.

This manual can be used in several ways.  If read from the beginning
to the end, it gives a good introduction into the library and how it
can be used in an application.  Forward references are included where
necessary.  Later on, the manual can be used as a reference manual to
get just the information needed about any particular interface of the
library.  Experienced programmers might want to start looking at the
examples at the end of the manual, and then only read up those parts
of the interface which are unclear.

@node Features
@section Features

GNU SASL might have a couple of advantages over other libraries doing
a similar job.

@table @asis
@item It's Free Software
Anybody can use, modify, and redistribute it under the terms of the
GNU General Public License.  The library can even be distributed under
the GNU Lesser General Public License.

@item It's thread-safe
No global variables are used and multiple library handles and session
handles may be used in parallel.

@item It's internationalized
It handles non-ASCII username and passwords and user visible strings
used in the library (error messages) can be translated into the users'
language.

@item It's portable
It should work on all Unix like operating systems, including Windows.
The library itself should be portable to any C89 system, not even
POSIX is required.

@end table

Note that the library do not implement any policy to decide whether a
certain user is ``authenticated'' or ``authorized'' or not.  Rather,
it uses a callback into the application to answer these questions.

@node SASL Overview
@section SASL Overview

This section describes SASL from a protocol point of view.

The Simple Authentication and Security Layer (SASL) is a method for
adding authentication support to connection-based protocols.  A
protocol includes a command for identifying and authenticating a user
to a server and for optionally negotiating a security layer for
subsequent protocol interactions.

The command has a required argument identifying a SASL mechanism.
SASL mechanisms are named by strings, from 1 to 20 characters in
length, consisting of upper-case letters, digits, hyphens, and/or
underscores.

If a server supports the requested mechanism, it initiates an
authentication protocol exchange.  This consists of a series of
server challenges and client responses that are specific to the
requested mechanism.  The challenges and responses are defined by the
mechanisms as binary tokens of arbitrary length.  The protocol's
profile then specifies how these binary tokens are then encoded for
transfer over the connection.

After receiving the authentication command or any client response, a
server may issue a challenge, indicate failure, or indicate
completion.  The protocol's profile specifies how the server
indicates which of the above it is doing.

After receiving a challenge, a client may issue a response or abort
the exchange.  The protocol's profile specifies how the client
indicates which of the above it is doing.

During the authentication protocol exchange, the mechanism performs
authentication, transmits an authorization identity (frequently known
as a userid) from the client to server, and negotiates the use of a
mechanism-specific security layer.  If the use of a security layer is
agreed upon, then the mechanism must also define or negotiate the
maximum cipher-text buffer size that each side is able to receive.

The transmitted authorization identity may be different than the
identity in the client's authentication credentials.  This permits
agents such as proxy servers to authenticate using their own
credentials, yet request the access privileges of the identity for
which they are proxying.  With any mechanism, transmitting an
authorization identity of the empty string directs the server to
derive an authorization identity from the client's authentication
credentials.

If use of a security layer is negotiated, it is applied to all
subsequent data sent over the connection.  The security layer takes
effect immediately following the last response of the authentication
exchange for data sent by the client and the completion indication
for data sent by the server.  Once the security layer is in effect,
the protocol stream is processed by the security layer into buffers
of cipher-text.  Each buffer is transferred over the connection as a
stream of octets prepended with a four octet field in network byte
order that represents the length of the following buffer.  The length
of the cipher-text buffer must be no larger than the maximum size
that was defined or negotiated by the other side.

@node Requirements
@section Requirements

The GNU SASL library does not have any required external dependencies,
but some optional features are enabled if you have a specific external
library.

@table @asis
@item LibNTLM
The NTLM mechanism requires the library LibNTLM,
@url{http://josefsson.org/libntlm/}.

@item GSS-API
The GSS-API mechanism requires a GSS-API library, such as GNU GSS
(@url{http://josefsson.org/gss/}, MIT Kerberos or Heimdal.

@item LibIDN
Processing of non-ASCII username and passwords requires the SASLprep
implementation in GNU LibIDN (@url{http://josefsson.org/libidn/}.
This is needed for full conformance with the latest SASL protocol
drafts, but is optional in the library for improved portability.

@item Libgcrypt
The GNU SASL library ships with its own cryptographic implementation,
but it can use the one in libgcrypt (@url{http://www.gnupg.org/}
instead, if it is available.  This is typically useful for desktop
machines which have libgcrypt installed.
@end table

The command-line interface to GNU SASL requires a POSIX or Windows
platform for network connectivity.  The command-line tool can make use
of GnuTLS (@url{http://josefsson.org/gnutls/} to support the STARTTLS
modes of IMAP and SMTP, but GnuTLS is not required.

Note that the library does not need a POSIX platform or network
connectivity.

@node Supported Platforms
@section Supported Platforms

GNU SASL has at some point in time been tested on the following
platforms.

@enumerate

@item Debian GNU/Linux 3.0 (Woody)
@cindex Debian

GCC 2.95.4 and GNU Make. This is the main development platform.
@code{alphaev67-unknown-linux-gnu}, @code{alphaev6-unknown-linux-gnu},
@code{arm-unknown-linux-gnu}, @code{hppa-unknown-linux-gnu},
@code{hppa64-unknown-linux-gnu}, @code{i686-pc-linux-gnu},
@code{ia64-unknown-linux-gnu}, @code{m68k-unknown-linux-gnu},
@code{mips-unknown-linux-gnu}, @code{mipsel-unknown-linux-gnu},
@code{powerpc-unknown-linux-gnu}, @code{s390-ibm-linux-gnu},
@code{sparc-unknown-linux-gnu}.

@item Debian GNU/Linux 2.1
@cindex Debian

GCC 2.95.1 and GNU Make. @code{armv4l-unknown-linux-gnu}.

@item Tru64 UNIX
@cindex Tru64

Tru64 UNIX C compiler and Tru64 Make. @code{alphaev67-dec-osf5.1},
@code{alphaev68-dec-osf5.1}.

@item SuSE Linux 7.1
@cindex SuSE

GCC 2.96 and GNU Make. @code{alphaev6-unknown-linux-gnu},
@code{alphaev67-unknown-linux-gnu}.

@item SuSE Linux 7.2a
@cindex SuSE Linux

GCC 3.0 and GNU Make. @code{ia64-unknown-linux-gnu}.

@item RedHat Linux 7.2
@cindex RedHat

GCC 2.96 and GNU Make. @code{alphaev6-unknown-linux-gnu},
@code{alphaev67-unknown-linux-gnu}, @code{ia64-unknown-linux-gnu}.

@item RedHat Linux 8.0
@cindex RedHat

GCC 3.2 and GNU Make. @code{i686-pc-linux-gnu}.

@item RedHat Advanced Server 2.1
@cindex RedHat Advanced Server

GCC 2.96 and GNU Make. @code{i686-pc-linux-gnu}.

@item Slackware Linux 8.0.01
@cindex RedHat

GCC 2.95.3 and GNU Make. @code{i686-pc-linux-gnu}.

@item Mandrake Linux 9.0
@cindex Mandrake

GCC 3.2 and GNU Make. @code{i686-pc-linux-gnu}.

@item IRIX 6.5
@cindex IRIX

MIPS C compiler, IRIX Make. @code{mips-sgi-irix6.5}.

@item AIX 4.3.2
@cindex AIX

IBM C for AIX compiler, AIX Make.  @code{rs6000-ibm-aix4.3.2.0}.

@item Microsoft Windows 2000 (Cygwin)
@cindex Windows

GCC 3.2, GNU make. @code{i686-pc-cygwin}.

@item HP-UX 11
@cindex HP-UX

HP-UX C compiler and HP Make. @code{ia64-hp-hpux11.22},
@code{hppa2.0w-hp-hpux11.11}.

@item SUN Solaris 2.8
@cindex Solaris

Sun WorkShop Compiler C 6.0 and SUN Make. @code{sparc-sun-solaris2.8}.

@item SUN Solaris 2.9
@cindex Solaris

Sun Forte Developer 7 C compiler and GNU
Make. @code{sparc-sun-solaris2.9}.

@item NetBSD 1.6
@cindex NetBSD

GCC 2.95.3 and GNU Make. @code{alpha-unknown-netbsd1.6},
@code{i386-unknown-netbsdelf1.6}.

@item OpenBSD 3.1 and 3.2
@cindex OpenBSD

GCC 2.95.3 and GNU Make. @code{alpha-unknown-openbsd3.1},
@code{i386-unknown-openbsd3.1}.

@item FreeBSD 4.7
@cindex FreeBSD

GCC 2.95.4 and GNU Make. @code{alpha-unknown-freebsd4.7},
@code{i386-unknown-freebsd4.7}.

@item Cross compiled to uClinux/uClibc on Motorola Coldfire.
@cindex Motorola Coldfire
@cindex uClinux
@cindex uClibc

GCC 3.4 and GNU Make @code{m68k-uclinux-elf}.

@end enumerate

If you port GNU SASL to a new platform, please report it to the author
so this list can be updated.

@node Getting help
@section Getting help

A mailing list where users may help each other exists, and you can
reach it by sending e-mail to @email{help-gsasl@@gnu.org}.  Archives
of the mailing list discussions, and an interface to manage
subscriptions, is available through the World Wide Web at
@url{http://lists.gnu.org/mailman/listinfo/help-gsasl}.

@node Commercial Support
@section Commercial Support

Commercial support is available for users of GNU SASL.  The kind of
support that can be purchased may include:

@itemize

@item Implement new features.
Such as a new SASL mechanism.

@item Port GNU SASL to new platforms.
This could include porting to an embedded platforms that may need
memory or size optimization.

@item Integrating SASL as a security environment in your existing project.

@item System design of components related to SASL.

@end itemize

If you are interested, please write to:

@verbatim
Simon Josefsson Datakonsult
Hagagatan 24
113 47 Stockholm
Sweden

E-mail: simon@josefsson.org
@end verbatim

If your company provide support related to GNU SASL and would like to
be mentioned here, contact the author (@pxref{Bug Reports}).

@node Downloading and Installing
@section Downloading and Installing
@cindex Installation
@cindex Download

The package can be downloaded from several places, including:

@url{http://josefsson.org/gsasl/releases/}

The latest version is stored in a file, e.g.,
@samp{gsasl-@value{VERSION}.tar.gz} where the @samp{@value{VERSION}}
value is the highest version number in the directory.

The package is then extracted, configured and built like many other
packages that use Autoconf.  For detailed information on configuring
and building it, refer to the @file{INSTALL} file that is part of the
distribution archive.

Here is an example terminal session that download, configure, build
and install the package.  You will need a few basic tools, such as
@samp{sh}, @samp{make} and @samp{cc}.

@example
$ wget -q http://josefsson.org/gsasl/releases/gsasl-@value{VERSION}.tar.gz
$ tar xfz gsasl-@value{VERSION}.tar.gz
$ cd gsasl-@value{VERSION}/
$ ./configure
...
$ make
...
$ make install
...
@end example

After that gsasl should be properly installed and ready for use.

A few @code{configure} options may be relevant, summarized in the
table.

@table @code

@item --disable-client
@itemx --disable-server
If your target system require a minimal implementation, you may wish
to disable the client or the server part of the code.  This do not
remove symbols from the library, so if you attempt to call an
application that uses server functions in a library built with
@code{--disable-server}, the function will return an error code.

@item --disable-obsolete
This remove backwards compatibility (@pxref{Old Functions}).  Use if
you want to limit the size of the library.

@item --disable-anonymous
@itemx --disable-external
@itemx --disable-plain
@itemx --disable-login
@itemx --disable-securid
@itemx --disable-ntlm
@itemx --disable-cram-md5
@itemx --disable-digest-md5
@itemx --disable-gssapi
@itemx --enable-kerberos_v5
Disable or enable individual mechanisms (@pxref{Mechanisms}).

@item --without-stringprep
Disable internationalized string processing.  Note that this will
result in a SASL library that is only compatible with RFC 2222.

@end table

For the complete list, refer to the output from @code{configure
--help}.

@node Bug Reports
@section Bug Reports
@cindex Reporting Bugs

If you think you have found a bug in GNU SASL, please investigate it
and report it.

@itemize @bullet

@item Please make sure that the bug is really in GNU SASL, and
preferably also check that it hasn't already been fixed in the latest
version.

@item You have to send us a test case that makes it possible for us to
reproduce the bug.

@item You also have to explain what is wrong; if you get a crash, or
if the results printed are not good and in that case, in what way.
Make sure that the bug report includes all information you would need
to fix this kind of bug for someone else.

@end itemize

Please make an effort to produce a self-contained report, with
something definite that can be tested or debugged.  Vague queries or
piecemeal messages are difficult to act on and don't help the
development effort.

If your bug report is good, we will do our best to help you to get a
corrected version of the software; if the bug report is poor, we won't
do anything about it (apart from asking you to send better bug
reports).

If you think something in this manual is unclear, or downright
incorrect, or if the language needs to be improved, please also send a
note.

Send your bug report to:

@center @samp{bug-gsasl@@gnu.org}

@node Contributing
@section Contributing
@cindex Contributing
@cindex Hacking

If you want to submit a patch for inclusion -- from solve a typo you
discovered, up to adding support for a new feature -- you should
submit it as a bug report (@pxref{Bug Reports}).  There are some
things that you can do to increase the chances for it to be included
in the official package.

Unless your patch is very small (say, under 10 lines) we require that
you assign the copyright of your work to the Free Software Foundation.
This is to protect the freedom of the project.  If you have not
already signed papers, we will send you the necessary information when
you submit your contribution.

For contributions that doesn't consist of actual programming code, the
only guidelines are common sense.  Use it.

For code contributions, a number of style guides will help you:

@itemize @bullet

@item Coding Style.
Follow the GNU Standards document (@pxref{top, GNU Coding Standards,,
standards}).

If you normally code using another coding standard, there is no
problem, but you should use @samp{indent} to reformat the code
(@pxref{top, GNU Indent,, indent}) before submitting your work.

@item Use the unified diff format @samp{diff -u}.

@item Return errors.
No reason whatsoever should abort the execution of the library.  Even
memory allocation errors, e.g. when malloc return NULL, should work
although result in an error code.

@item Design with thread safety in mind.
Don't use global variables.  Don't even write to per-handle global
variables unless the documented behaviour of the function you write is
to write to the per-handle global variable.

@item Avoid using the C math library.
It causes problems for embedded implementations, and in most
situations it is very easy to avoid using it.

@item Document your functions.
Use comments before each function headers, that, if properly
formatted, are extracted into Texinfo manuals and GTK-DOC web pages.

@item Supply a ChangeLog and NEWS entries, where appropriate.

@end itemize

@c **********************************************************
@c *******************  Preparation  ************************
@c **********************************************************
@node Preparation
@chapter Preparation

To use GNU SASL, you have to perform some changes to your sources and
the build system.  The necessary changes are small and explained in
the following sections.  At the end of this chapter, it is described
how the library is initialized, and how the requirements of the
library are verified.

A faster way to find out how to adapt your application for use with
GNU SASL may be to look at the examples at the end of this manual
(@pxref{Examples}).

@menu
* Header::
* Initialization::
* Version Check::
* Building the source::
* Autoconf tests::
@end menu

@node Header
@section Header

All interfaces (data types and functions) of the library are defined
in the header file `gsasl.h'.  You must include this in all programs
using the library, either directly or through some other header file,
like this:

@example
#include <gsasl.h>
@end example

The name space is @code{gsasl_*} for function names, @code{Gsasl*} for
data types and @code{GSASL_*} for other symbols.  In addition the same
name prefixes with one prepended underscore are reserved for internal
use and should never be used by an application.

@node Initialization
@section Initialization

The library must be initialized before it can be used.  The library is
initialized by calling @code{gsasl_init} (@pxref{Global Functions}).
The resources allocated by the initialization process can be released
if the application no longer has a need to call `Libgsasl' functions,
this is done by calling @code{gsasl_done}.  For example:

@example
int
main (int argc, char *argv[])
@{
  Gsasl *ctx = NULL;
  int rc;
...
  rc = gsasl_init (&ctx);
  if (rc != GSASL_OK)
    @{
      printf ("SASL initialization failure (%d): %s\n",
              rc, gsasl_strerror (rc));
      return 1;
    @}
...
@end example

In order to make error messages from @code{gsasl_strerror} be
translated (@pxref{Top,,,gettext,GNU Gettext}) the application must
set the current locale using @code{setlocale} before calling
@code{gsasl_init}.  For example:

@example
int
main (int argc, char *argv[])
@{
  Gsasl *ctx = NULL;
  int rc;
...
  setlocale (LC_ALL, "");
...
  rc = gsasl_init (&ctx);
  if (rc != GSASL_OK)
    @{
      printf (gettext ("SASL initialization failure (%d): %s\n"),
              rc, gsasl_strerror (rc));
      return 1;
    @}
...
@end example

In order to take advantage of the secure memory features in
Libgcrypt@footnote{Note that GNU SASL normally use its own internal
implementation of the cryptographic functions.  Take care to verify
that GNU SASL really use Libgcrypt, if this is what you want.}, you
need to initialize secure memory in your application, and for some
platforms even make your application setuid root.  See the Libgcrypt
documentation for more information.  Example code to initialize secure
memory in your code:

@example
#include <gcrypt.h>
...
int
main (int argc, char *argv[])
@{
  Gsasl *ctx = NULL;
  int rc;
...
  /* Check version of libgcrypt. */
  if (!gcry_check_version (GCRYPT_VERSION))
    die ("version mismatch\n");

  /* Allocate a pool of 16k secure memory.  This also drops priviliges
     on some systems. */
  gcry_control (GCRYCTL_INIT_SECMEM, 16384, 0);

  /* Tell Libgcrypt that initialization has completed. */
  gcry_control (GCRYCTL_INITIALIZATION_FINISHED, 0);
...
  rc = gsasl_init (&ctx);
  if (rc != GSASL_OK)
    @{
      printf ("SASL initialization failure (%d): %s\n",
              rc, gsasl_strerror (rc));
      return 1;
    @}
...
@end example

If you do not do this, keying material will not be allocated in secure
memory (which for most application is not the biggest secure problem
anyway).  Note that the GNU SASL Library has not been audited to make
sure it only ever stores passwords or keys in secure memory.

@node Version Check
@section Version Check

It is often desirable to check that the version of the library used is
indeed one which fits all requirements.  Even with binary
compatibility new features may have been introduced but due to problem
with the dynamic linker an old version is actually used.  So you may
want to check that the version is okay right after program startup.

@include texi/gsasl_check_version.texi

The normal way to use the function is to put something similar to the
following early in your @code{main}:

@example
  if (!gsasl_check_version (GSASL_VERSION))
    @{
      printf ("gsasl_check_version failed:\n"
              "Header file incompatible with shared library.\n");
      exit(1);
    @}
@end example

@node Building the source
@section Building the source
@cindex Compiling your application

If you want to compile a source file including the `gsasl.h' header
file, you must make sure that the compiler can find it in the
directory hierarchy.  This is accomplished by adding the path to the
directory in which the header file is located to the compilers include
file search path (via the @option{-I} option).

However, the path to the include file is determined at the time the
source is configured.  To solve this problem, the library uses the
external package @command{pkg-config} that knows the path to the
include file and other configuration options.  The options that need
to be added to the compiler invocation at compile time are output by
the @option{--cflags} option to @command{pkg-config libgsasl}.  The
following example shows how it can be used at the command line:

@example
gcc -c foo.c `pkg-config libgsasl --cflags`
@end example

Adding the output of @samp{pkg-config libgsasl --cflags} to the
compilers command line will ensure that the compiler can find the
`gsasl.h' header file.

A similar problem occurs when linking the program with the library.
Again, the compiler has to find the library files.  For this to work,
the path to the library files has to be added to the library search path
(via the @option{-L} option).  For this, the option @option{--libs} to
@command{pkg-config libgsasl} can be used.  For convenience, this option
also outputs all other options that are required to link the program
with the `libgsasl' libarary (for instance, the @samp{-lidn}
option).  The example shows how to link @file{foo.o} with the `libgsasl'
library to a program @command{foo}.

@example
gcc -o foo foo.o `pkg-config libgsasl --libs`
@end example

Of course you can also combine both examples to a single command by
specifying both options to @command{pkg-config}:

@example
gcc -o foo foo.c `pkg-config libgsasl --cflags --libs`
@end example

@node Autoconf tests
@section Autoconf tests
@cindex Autoconf tests
@cindex Configure tests

If you work on a project that uses Autoconf (@pxref{top, GNU
Autoconf,, autoconf}) to help find installed libraries, the
suggestions in the previous section are not the entire story.  There
are a few methods to detect and incorporate the GNU SASL Library into
your Autoconf based package.  The preferred approach, is to use
Libtool in your project, and use the normal Autoconf header file and
library tests.

@subsection Autoconf test via @samp{pkg-config}

If your audience is a typical GNU/Linux desktop, you can often assume
they have the @samp{pkg-config} tool installed, in which you can use
its Autoconf M4 macro to find and set up your package for use with
Libgsasl.  The following illustrate this scenario.

@example
AC_ARG_ENABLE(gsasl,
        AC_HELP_STRING([--disable-gsasl], [don't use GNU SASL]),
        gsasl=$enableval)
if test "$gsal" != "no" ; then
        PKG_CHECK_MODULES(GSASL, libgsasl >= @value{VERSION},
                        [gsasl=yes],
                        [gsasl=no])
        if test "$gsasl" != "yes" ; then
                sal=no
                AC_MSG_WARN([Cannot find GNU SASL, disabling])
        else
                gsasl=yes
                AC_DEFINE(USE_GSASL, 1, [Define to 1 if you want GNU SASL.])
        fi
fi
AC_MSG_CHECKING([if GNU SASL should be used])
AC_MSG_RESULT($gsasl)
@end example

@subsection Standalone Autoconf test using Libtool

If your package uses Libtool(@pxref{top, GNU Libtool,, libtool}), you
can use the normal Autoconf tests to find Libgsasl and rely on the
Libtool dependency tracking to include the proper dependency libraries
(e.g., Libidn).  The following illustrate this scenario.

@example
AC_CHECK_HEADER(gsasl.h,
        AC_CHECK_LIB(gsasl, gsasl_check_version,
                [gsasl=yes AC_SUBST(GSASL_LIBS, -lgsasl)],
                gsasl=no),
        gsasl=no)
AC_ARG_ENABLE(gsasl,
        AC_HELP_STRING([--disable-gsasl], [don't use GNU SASL]),
        gsasl=$enableval)
if test "$gsasl" != "no" ; then
        AC_DEFINE(USE_SASL, 1, [Define to 1 if you want GNU SASL.])
else
        AC_MSG_WARN([Cannot find GNU SASL, diabling])
fi
AC_MSG_CHECKING([if GNU SASL should be used])
AC_MSG_RESULT($gsasl)
@end example

@c **********************************************************
@c *****************  Using the Library  ********************
@c **********************************************************
@node Using the Library
@chapter Using the Library

Your application's use of the library can be roughly modeled into the
following steps: initialize the library, optionally specify the
callback, perform the authentication, and finally clean up.  The
following image illustrate this.

@image{controlflow,15cm,5cm}

The third step may look the most complex, but for a simple client it
will actually not involve any code.  If your application need to
handle several concurrent clients, or if it is a server that need to
serve many clients simultaneous, things do get a bit more complicated.

For illustration, we will write a simple client.  Writing a server
would be similar, the only difference is that, later on, instead of
supplying username or passwords, you need to decide whether someone
should be allowed to log in or not.  The code for what we have
discussed so far make up our @code{main} function in our client
(@pxref{Example 1}):

@example
int main (int argc, char *argv[])
@{
  Gsasl *ctx = NULL;
  int rc;

  if ((rc = gsasl_init (&ctx)) != GSASL_OK)
    @{
      printf ("Cannot initialize libgsasl (%d): %s",
              rc, gsasl_strerror (rc));
      return 1;
    @}

  client (ctx);

  gsasl_done (ctx);

  return 0;
@}
@end example

Here, the call to the function @code{client} correspond to the third
step in the image above.

For a more complicated application, that have several clients running
simultaneous, instead of simply calling @code{client}, it may have
created new threads for each session, and call @code{client} within
each thread.  The library is thread safe.

An actual authentication session is more complicated than what we have
seen so far.  The steps that make up it are: decide which mechanism to
use, start the session, optionally specify the callback, optionally
set any properties, perform the authentication loop, and clean up.
Naturally, your application will start to talk its own protocol (e.g.,
SMTP or IMAP) after these steps have concluded.

The authentication loop is based on sending tokens (typically short
messages encoded in base 64) back and forth between the client and
server.  It continue until authentication succeeds or there is an
error.  The format of the data to transfer, the number of iterations
in the loop, and other details are specified by each mechanism.  The
goal of the library is to isolate your application from the details of
all different mechanisms.

Note that the library do not send data to the server itself, but
return it in an buffer.  You must send it to the server yourself,
according to an application protocol profile.  For example, the
@acronym{SASL} application protocol profile for @acronym{SMTP} is
described in @acronym{RFC} 2554.

The following image illustrate the steps we have been talking about.

@image{controlflow2,16cm,12cm}

We will now show the implementation of the @code{client} function used
before.

@example
void client (Gsasl *ctx)
@{
  Gsasl_session *session;
  const char *mech = "PLAIN";
  int rc;

  /* Create new authentication session. */
  if ((rc = gsasl_client_start (ctx, mech, &session)) != GSASL_OK)
    @{
      printf ("Cannot initialize client (%d): %s\n",
              rc, gsasl_strerror (rc));
      return;
    @}

  /* Set username and password in session handle.  This info will be
     lost when this session is deallocated below.  */
  gsasl_property_set (session, GSASL_AUTHID, "jas");
  gsasl_property_set (session, GSASL_PASSWORD, "secret");

  /* Do it. */
  client_authenticate (ctx, session);

  /* Cleanup. */
  gsasl_finish (session);
@}
@end example

This function is responsible for deciding which mechanism to use.  In
this case, the @samp{PLAIN} mechanism is hard coded, but you will see
later how this can be made more flexible.  The function create a new
session, store the username and password in the session handle, then
call another function @code{client_authenticate} to handle the
authentication loop, and end by cleaning up.  Let's continue with the
implementation of @code{client_authenticate}.

@example
void client_authenticate (Gsasl * ctx, Gsasl_session * session)
@{
  char buf[BUFSIZ] = "";
  char *p;
  int rc;

  /* This loop mimic a protocol where the server get to send data
     first. */

  do
    @{
      printf ("Input base64 encoded data from server:\n");
      fgets (buf, sizeof (buf) - 1, stdin);
      if (buf[strlen (buf) - 1] == '\n')
        buf[strlen (buf) - 1] = '\0';

      rc = gsasl_step64 (session, buf, &p);

      if (rc == GSASL_NEEDS_MORE || rc == GSASL_OK)
        @{
          printf ("Output:\n%s\n", p);
          free (p);
        @}
    @}
  while (rc == GSASL_NEEDS_MORE);

  printf ("\n");

  if (rc != GSASL_OK)
    @{
      printf ("Authentication error (%d): %s\n",
              rc, gsasl_strerror (rc));
      return;
    @}

  /* The client is done.  Here you would typically check if the
     server let the client in.  If not, you could try again. */

  printf ("If server accepted us, we're done.\n");
@}
@end example

This last function need to be discussed in some detail.  First, you
should be aware that there are two versions of this function, that
differ in a subtle way.  The version above (@pxref{Example 2}) is used
for application profiles where the server send data first.  For some
mechanisms, this may waste a roundtrip, because the server need input
from the client to proceed.  Therefor, today the recommended approach
is to permit client to send data first (@pxref{Example 1}).  Which
version you should use depend on which application protocol you are
implementing.

Further, you should realize that it is bad programming style to use a
fixed size buffer.  On GNU systems, you may use the @code{getline}
functions instead of @code{fgets}.  However, in practice, there are
few mechanisms that use very large tokens.  In typical configurations,
the mechanism with the largest tokens (GSSAPI) can use at least 500
bytes.  A fixed buffer size of 8192 bytes may thus be sufficient for
now.  But don't say I didn't warn you, when a future mechanism doesn't
work in your application, because of a fixed size buffer.

The @code{gsasl_step64} (and of course also @code{gasl_step}) return
two non-error return codes.  @code{GSASL_OK} is used for success,
indicating that the library consider the authentication finished.
That may include a successful server authentication, depending on the
mechanism.  You must not let the client continue to the application
protocol part unless you receive @code{GSASL_OK} from these functions.
In particular, don't be fooled into believing authentication were
successful if the server reply ``OK'' but these function has failed
with an error.  The server may have been hacked, and could be tricking
you into sending confidential data, without having successfully
authenticated the server.

The non-error return code @code{GSASL_NEEDS_MORE} is used to signal to
your application that you should send the output token to the peer,
and wait for a new token, and do another iteration.  If the server
conclude the authentication process, with no data, you should call
@code{gsasl_step64} (or @code{gsasl_step}) specifying a zero-length
token.

If the functions (@code{gsasl_step} and @code{gsasl_step64}) return
any non-error code, the content of the output buffer is undefined.
Otherwise, it is the callers responsibility to deallocate the buffer,
by calling @code{free}.  Note that in some situations, where the
buffer is empty, @code{NULL} is returned as the buffer value.  You
should treat this as an empty buffer.

@section Choosing a mechanism

Our earlier code was hard coded to use a specific mechanism.  This is
rarely a good idea.  Instead, it is recommended to select the best
mechanism available from the list of mechanism supported by the
server.  Note that without TLS or similar, the list may have been
maliciously altered, by an attacker.  This means that you should abort
if you cannot find any mechanism that exceeds your minimum security
level.  There is a function @code{gsasl_client_suggest_mechanism}
(@pxref{Global Functions}) that will try to pick the ``best''
available mechanism from a list of mechanisms.  Our simple interactive
example client (@pxref{Example 3}) include the following function to
decide which mechanism to use.  Note that the code doesn't blindly use
what is returned from @code{gsasl_client_suggest_mechanism}, but
rather let some logic (in this case the user, through an interactive
query) decide which mechanism is acceptable.

@example
const char *client_mechanism (Gsasl *ctx)
@{
  static char mech[GSASL_MAX_MECHANISM_SIZE + 1] = "";
  char mechlist[BUFSIZ] = "";
  const char *suggestion;

  printf ("Enter list of mechanism that server support, separate by SPC:\n");
  fgets (mechlist, sizeof (mechlist) - 1, stdin);

  suggestion = gsasl_client_suggest_mechanism (ctx, mechlist);
  if (suggestion)
    printf ("Library suggest use of `%s'.\n", suggestion);

  printf ("Enter mechanism to use:\n");
  fgets (mech, sizeof (mech) - 1, stdin);
  mech[strlen (mech) - 1] = '\0';

  return mech;
@}
@end example

When running this example code, it might look like in the following
output.

@example
Enter list of mechanism that server support, separate by SPC:
CRAM-MD5 DIGEST-MD5 GSSAPI FOO BAR
Library suggest use of `GSSAPI'.
Enter mechanism to use:
CRAM-MD5
Input base64 encoded data from server:
Zm5vcmQ=
Output:
amFzIDkyY2U1NWE5MTM2ZTY4NzEyMTUyZTFjYmFmNjVkZjgx

If server accepted us, we're done.
@end example

@section Using a callback

Our earlier code specified the username and password before the
authentication loop, as in:

@example
  gsasl_property_set (ctx, GSASL_AUTHID, "jas");
  gsasl_property_set (ctx, GSASL_PASSWORD, "secret");
@end example

This may work for simple mechanisms, that only ever need an username
and a password.  But some mechanism require more information, such as
an authorization identity, a special PIN or passcode, a realm, a
hostname, a service name, or an anonymous identifier.  Querying the
user for all that information, without knowing exactly which of it is
really needed will result in a poor user interface.  The user should
not have to input private information, if it isn't required.

The approach is a bad idea for another reason.  What if the server
abort the authentication process?  Then your application have already
queried the user for a username and password.  It would be better if
you only asked the user for this information, annoying to input, when
it is known to be needed.

A better approach to this problem is to use a callback.  Then the
mechanism may query your application whenever it need some
information, like the username and password.  It will only do this at
the precise step in the authentication when the information is
actually needed.  Further, if the user abort, e.g., a password prompt,
the mechanism is directly informed of this (because it invoked the
callback), and could recover somehow.

Our final example (@pxref{Example 4}) specify a callback function,
inside @code{main} as below.

@example
  /* Set the callback handler for the library. */
  gsasl_callback_set (ctx, callback);
@end example

The function itself is implemented as follows.

@example
int callback (Gsasl * ctx, Gsasl_session * sctx, Gsasl_property prop)
@{
  char buf[BUFSIZ] = "";
  int rc = GSASL_NO_CALLBACK;

  /* Get user info from user. */

  printf ("Callback invoked, for property %d.\n", prop);

  switch (prop)
    @{
    case GSASL_PASSCODE:
      printf ("Enter passcode:\n");
      fgets (buf, sizeof (buf) - 1, stdin);
      buf[strlen (buf) - 1] = '\0';

      gsasl_property_set (sctx, GSASL_PASSCODE, buf);
      rc = GSASL_OK;
      break;

    case GSASL_AUTHID:
      printf ("Enter username:\n");
      fgets (buf, sizeof (buf) - 1, stdin);
      buf[strlen (buf) - 1] = '\0';

      gsasl_property_set (sctx, GSASL_AUTHID, buf);
      rc = GSASL_OK;
      break;

    default:
      printf ("Unknown property!  Don't worry.\n");
      break;
    @}

  return rc;
@}
@end example

Again, it is bad style to use a fixed size buffer.  Mmm'kay.

Which properties you should handle is up to you.  If you don't know
how to respond to a certain property, simply return
@code{GSASL_NO_CALLBACK}.  The basic properties to support are
authentication identity (@code{GSASL_AUTHID}), authorization identity
(@code{GSASL_AUTHZID}), and password (@code{GSASL_PASSWORD}).  See
@xref{Properties}, for the list of all properties, and what your
callback should (ideally) do for them, and which properties each
mechanism require in order to work.

@c **********************************************************
@c *******************  Properties  *************************
@c **********************************************************
@node Properties
@chapter Properties

@c FIXME: Write introductions to properties.  Discuss differences
@c between client and server properties.  Discuss validating
@c meta-properties.

Properties with associated data:

@itemize

@item @code{GSASL_AUTHID}

The authentication identity.

@item @code{GSASL_AUTHZID}

The authorization identity.

@item @code{GSASL_PASSWORD}

The password of the authentication identity.

@item @code{GSASL_ANONYMOUS_TOKEN}

The anonymous token.  This is typically the email address of the user.

@item @code{GSASL_SERVICE}

The registered GSSAPI service name of the application service,
e.g. ``imap''.  While the names are registered for GSSAPI, other
mechanisms such as DIGEST-MD5 may also use this.

@item @code{GSASL_HOSTNAME}

Should be the local host name of the machine.

@item @code{GSASL_GSSAPI_DISPLAY_NAME}

Contain the GSSAPI ``display name'', set by the server GSSAPI
mechanism.  Typically you retrieve this property in your callback,
when invoked for @code{GSASL_VALIDATE_GSSAPI}.

@item @code{GSASL_REALM}

The name of the authentication domain.  This is used by several
mechanisms, including DIGEST-MD5, GSS-API, KERBEROS_V5 and NTLM.

@item @code{GSASL_PASSCODE}

The SecurID passcode.

@item @code{GSASL_PIN}

The SecurID personal identification number (PIN).

@item @code{GSASL_SUGGESTED_PIN}

A SecurID personal identification number (PIN) suggested by the server.

@end itemize

Abstract properties, used to trigger the callback, typically used in
servers to validate client credentials:

@itemize

@item @code{GSASL_VALIDATE_SIMPLE}

You may retrieve GSASL_AUTHID, GSASL_AUTHZID and GSASL_PASSWORD and
use them to make an authentication and authorization decision.

@item @code{GSASL_VALIDATE_EXTERNAL}

Used by EXTERNAL mechanism on the server side to validate the client.
The GSASL_AUTHID will contain the authorization identity of the
client.

@item @code{GSASL_VALIDATE_ANONYMOUS}

Used by ANONYMOUS mechanism on the server side to validate the client.
The GSASL_ANONYMOUS_TOKEN will contain token that identity the client.

@item @code{GSASL_VALIDATE_GSSAPI}

Used by the GSSAPI mechanism on the server side, to validate the
client.  You may retrieve the authorization identity from
GSASL_AUTHZID and the GSS-API display name from
GSASL_GSSAPI_DISPLAY_NAME.

@item @code{GSASL_VALIDATE_SECURID}

Used by SECURID mechanism on the server side to validate client.  The
GSASL_AUTHID, GSASL_AUTHZID, GSASL_PASSCODE, and GSASL_PIN will be
set.  It can return GSASL_SECURID_SERVER_NEED_ADDITIONAL_PASSCODE to
ask the client to supply another passcode, and
GSASL_SECURID_SERVER_NEED_NEW_PIN to require the client to supply a
new PIN code.

@end itemize


@c **********************************************************
@c *******************  Mechanisms  *************************
@c **********************************************************
@node Mechanisms
@chapter Mechanisms

Different SASL mechanisms have different requirements on the
application using it.  To handle these differences the library can use
a callback function into your application in several different ways.
Some mechanisms, such as @samp{PLAIN}, are simple to explain and use.
The client callback query the user for a username and password.  The
server callback hand the username and password into any local policy
deciding authentication system (such as @file{/etc/passwd} via PAM).

Mechanism such as @samp{CRAM-MD5} and @samp{DIGEST-MD5} uses hashed
passwords.  The client callback behaviour is the same as for PLAIN.
However, the server do not receive the plain text password over the
network but rather a hash of it.  Existing policy deciding systems
like PAM cannot handle this, so the server callback for these
mechanisms are more complicated.

Further, mechanisms like GSSAPI (Kerberos 5) assume a specific
authentication system.  In theory this means that the SASL library
would not need to interact with the application, but rather call this
specific authentication system directly.  However, some callbacks are
supported anyway, to modify the behaviour of how the specific
authentication system is used (i.e., to handle ``super-user'' login as
some other user).

Some mechanisms, like @samp{EXTERNAL} and @samp{ANONYMOUS} are
entirely dependent on callbacks.

@menu
* EXTERNAL::                Authentication via out of band information.
* ANONYMOUS::               Mechanism for anonymous access to resources.
* PLAIN::                   Clear text username and password.
* LOGIN::                   Non-standard clear text username and password.
* CRAM-MD5::                Challenge-Response Authentication Mechanism.
* DIGEST-MD5::              Digest Authentication.
* NTLM::                    Microsoft NTLM authentication.
* SECURID::                 Authentication using tokens.
* GSSAPI::                  GSSAPI (Kerberos 5) authentication.
* KERBEROS_V5::             Experimental KERBEROS_V5 authentication.
@end menu

@node EXTERNAL
@section The EXTERNAL mechanism

The EXTERNAL mechanism is used to authenticate a user to a server
based on out-of-band authentication.  EXTERNAL is typically used over
TLS authenticated channels.  Note that in the server, you need to make
sure that TLS actually authenticated the client successfully.  It is
normally not sufficient that TLS is used, since they also support
anonymous modes.

In the client, this mechanism is always enabled, and will send the
@code{GSASL_AUTHZID} property as the authorization name to the server,
if the property is set.  If the property is not set, the empty
authorization name is sent.  You need not implement a callback.

In the server, this mechanism will invoke the
@code{GSASL_VALIDATE_EXTERNAL} callback to decide whether the client
is authenticated and authorized to log in.  Your callback can retrieve
the @code{GSASL_AUTHZID} property to inspect the requested
authorization name from the client.

@node ANONYMOUS
@section The ANONYMOUS mechanism

The ANONYMOUS mechanism is used to ``authenticate'' clients to
anonymous services; or rather, just indicate that the client wishes to
use the service anonymously.  The client sends a token, usually her
email address, which serve the purpose of some trace information
suitable for log files.  The token is not permitted to be empty.

In the client, this mechanism is always enabled, and will send the
@code{GSASL_ANONYMOUS_TOKEN} property as the trace information to the
server.

In the server, this mechanism will invoke the
@code{GSASL_VALIDATE_ANONYMOUS} callback to decide whether the client
should be permitted to log in.  Your callback can retrieve the
@code{GSASL_ANONYMOUS_TOKEN} property to, for example, save it in a
log file.  The token is normally not used to decide whether the client
should be permitted to log in or not.

@node PLAIN
@section The PLAIN mechanism

The PLAIN mechanism uses username and password to authenticate users.
Two user names are relevant.  The first, the authentication identity,
indicate the credential holder, i.e., whom the provided password
belongs to.  The second, the authorization identity, is typically
empty, to indicate that the user requests to log on to the server as
herself.  However, if the authorization identity is not empty, the
server should decide whether the authenticated user may log on as the
authorization identity.  Normally, only ``super-user'' accounts such
as @samp{admin} or similar should be allowed this.

In the client, this mechanism is always enabled, and require the
@code{GSASL_AUTHID} and @code{GSASL_PASSWORD} properties.  If set,
@code{GSASL_AUTHZID} will also be used.

In the server, the mechanism is always enabled.  Two approaches to
authenticate and authorize the client is provided.

In the first approach, the server side of the mechanism will invoke
the @code{GSASL_VALIDATE_SIMPLE} callback property to decide whether
the client should be accepted or not.  The callback may inspect the
@code{GSASL_AUTHID}, @code{GSASL_AUTHID}, and @code{GSASL_PASSWORD}
properties.  These properties values will be normalized.

If the first approach fails (because, e.g., your callback return
@samp{GSASL_NO_CALLBACK} to signal that it does not implement
@code{GSASL_VALIDATE_SIMPLE}) the mechanism will continue to query the
application for a password, via the @code{GSASL_PASSWORD} property.
Your callback may use the @code{GSASL_AUTHID} and @code{GSASL_AUTHZID}
properties to select the proper password.  The password is then
normalized and compared to the client credential.

Which approach to use?  If your database store hashed passwords, you
have no option, but must use the first approach.  If passwords in your
user database are stored in prepared (@acronym{SASLprep}) form, the
first approach will be faster.  If you do not have prepared passwords
available, you can use the second approach to make sure the password
is prepared properly before comparison.

@node LOGIN
@section The LOGIN mechanism

The LOGIN mechanism is a non-standard mechanism, and is similar to the
PLAIN mechanism except that LOGIN lack the support for authorization
identities.  Always use PLAIN instead of LOGIN in new applications.

The callback behaviour is the same as for PLAIN, except that
@code{GSASL_AUTHZID} is not used nor required, and that the server do
not normalize the password using @acronym{SASLprep}.

@xref{Use of SASLprep in LOGIN}, for a proposed clarification of the
interpretation of a hypothetical LOGIN specification.

@node CRAM-MD5
@section The CRAM-MD5 mechanism

The CRAM-MD5 is a widely used, but officially deprecated (apparently
in favor of DIGEST-MD5), challenge-response mechanism that transfer
hashed passwords instead of clear text passwords.  For insecure
channels (e.g., when @acronym{TLS} is not used), it is safer than
PLAIN.  The CRAM-MD5 mechanism do not support authorization
identities; making the relationship between CRAM-MD5 and DIGEST-MD5
similar to the relationship between LOGIN and PLAIN.

The disadvantage with hashed passwords is that the server cannot use
normal authentication infrastructures such as PAM, because the server
must have access to the correct password in order to validate an
authentication attempt.

In the client, this mechanism is always enabled, and require the
@code{GSASL_AUTHID} and @code{GSASL_PASSWORD} properties.

In the server, the mechanism will invoke the @code{GSASL_PASSWORD}
callback, which may use the @code{GSASL_AUTHID} property to determine
which users' password should be used.  The @code{GSASL_AUTHID} will be
in normalized form.  The server will then normalize the returned
password, and compare the client response with the computed correct
response, and accept the user accordingly.

@xref{Use of SASLprep in CRAM-MD5}, for a clarification on the
interpretation of the CRAM-MD5 specification that this implementation
rely on.

@node DIGEST-MD5
@section The DIGEST-MD5 mechanism

The DIGEST-MD5 mechanism is based on repeated hashing using MD5, which
after the MD5 break may be argued to be weaker than HMAC-MD5, but
supports more features.  For example, authorization identities and
data integrity and privacy protection are supported.  Like CRAM-MD5,
only a hashed password is transfered.  Consequently, DIGEST-MD5 need
access to the correct password (although it may be hashed, another
improvement compared to CRAM-MD5) to verify the client response.
Alas, this make it impossible to use, e.g., @acronym{PAM} on the
server side.

In the client, this mechanism is always enabled, and require the
@code{GSASL_AUTHID}, @code{GSASL_PASSWORD}, @code{GSASL_SERVICE}, and
@code{GSASL_HOSTNAME} properties.  If set, @code{GSASL_AUTHZID} and
@code{GSASL_REALM} will also be used.

In the server, the mechanism will invoke the @code{GSASL_PASSWORD}
callback, which may use the @code{GSASL_AUTHID}, @code{GSASL_AUTHZID}
and @code{GSASL_REALM} properties to determine which users' password
should be used.  The server will then compare the client response with
a computed correct response, and accept the user accordingly.

Currently only the authentication quality of service is implemented.
In other words, payload integrity or privacy protection are not
supported.  Consequently, there are no properties for the maximum
buffer size, quality of protection, and cipher fields.

@node NTLM
@section The NTLM mechanism

The NTLM is a non-standard mechanism.  Do not use it in new
applications, and do not expect it to be secure.  Currently only the
client side is supported.

In the client, this mechanism is always enabled, and require the
@code{GSASL_AUTHID} and @code{GSASL_PASSWORD} properties.  It will set
the @samp{domain} field in the NTLM request to the value of
@code{GSASL_REALM}.  Some servers reportedly need non-empty but
arbitrary values in that field.

@node SECURID
@section The SECURID mechanism

The SECURID mechanism uses authentication and authorization identity
together with a passcode from a hardware token to authenticate users.

In the client, this mechanism is always enabled, and require the
@code{GSASL_AUTHID} and @code{GSASL_PASSCODE} properties.  If set,
@code{GSASL_AUTHZID} will also be used.  If the server requests it,
the @code{GSASL_PIN} property is also required, and its callback may
inspect the @code{GSASL_SUGGESTED_PIN} property to discover a
server-provided PIN to use.

In the server, this mechanism will invoke the
@code{GSASL_VALIDATE_SECURID} callback.  The callback may inspect the
@code{GSASL_AUTHID}, @code{GSASL_AUTHZID}, and @code{GSASL_PASSCODE}
properties.  The callback can return
@code{GSASL_SECURID_SERVER_NEED_ADDITIONAL_PASSCODE} to ask for
another additional passcode from the client.  The callback can return
@code{GSASL_SECURID_SERVER_NEED_NEW_PIN} to ask for a new PIN code
from the client, in which case it may also set the
@code{GSASL_SUGGESTED_PIN} property to indicate a recommended new PIN.
If the callbacks has invoked again, after having returned
@code{GSASL_SECURID_SERVER_NEED_NEW_PIN}, it may also inspect the
@code{GSASL_PIN} property, in addition to the other properties, to
find out the client selected PIN code.

@node GSSAPI
@section The GSSAPI mechanism

GSS-API is a framework, similar to SASL, for authentication.  The
GSSAPI mechanism only support the Kerberos 5 GSS-API mechanism,
though.  (A new SASL mechanism to support non-Kerberos 5 GSS-API
mechanisms may be supported in the future.)

In the client, the mechanism is enabled only if the user has acquired
credentials (i.e., a ticket granting ticket), and require the
@code{GSASL_AUTHID}, @code{GSASL_SERVICE}, and @code{GSASL_HOSTNAME}
properties.

In the server, the mechanism require the @code{GSASL_SERVICE}, and
@code{GSASL_HOSTNAME} properties, and will invoke the
@code{GSASL_VALIDATE_GSSAPI} callback in order to validate the user.
The callback may inspect the @code{GSASL_AUTHZID} and
@code{GSASL_GSSAPI_DISPLAY_NAME} properties to decide whether to
authorize the user.  Note that authentication is performed by the
GSS-API library.

XXX: explain more about quality of service, maximum buffer size, etc.

@node KERBEROS_V5
@section The KERBEROS_V5 mechanism

The KERBEROS_V5 is an experimental mechanism, the protocol
specification is available on the GNU SASL homepage.  It can operate
in three modes, non-infrastructure mode, infrastructure mode and
proxied infrastructure mode.  Currently only non-infrastructure mode
is supported.

In the non-infrastructure mode, it works as a superset of most
features provided by PLAIN, CRAM-MD5, DIGEST-MD5 and GSSAPI while at
the same time building on what is believed to be proven technology
(the RFC 1510 network security system).  In the non-infrastructure
mode, the client must specify (via callbacks) the name of the user,
and optionally the server name and realm.  The server must be able to
retrieve passwords given the name of the user.

In the infrastructure mode (proxied or otherwise), it allows clients
and servers to authenticate via SASL in an RFC 1510 environment, using
a trusted third party, a ``Key Distribution Central''.  In the normal
mode, clients aquire tickets out of band and then invokes a one
roundtrip AP-REQ and AP-REP exchange.  In the proxied mode, which can
be used by clients without IP addresses or without connectivity to the
KDC (e.g., when the KDC is IPv4 and the client is IPV6-only), the
client uses the server to proxy ticket requests and finishes with the
AP-REQ/AP-REP exchange.  In infrastructure mode (proxied or
otherwise), the client nor server need to implement any callbacks
(this will likely change later, to allow a server to authorize users,
similar to the GSSAPI callback).

XXX: update when implementation has matured

@c **********************************************************
@c *****************  Global Functions  *********************
@c **********************************************************
@node Global Functions
@chapter Global Functions

@include texi/init.c.texi
@include texi/done.c.texi
@include texi/listmech.c.texi
@include texi/supportp.c.texi
@include texi/suggest.c.texi
@include texi/register.c.texi


@c **********************************************************
@c ******************  Callback Functions  ******************
@c **********************************************************
@node Callback Functions
@chapter Callback Functions
@cindex Callbacks

The callback is used by mechanisms to retrieve information, such as
username and password, from the application.  In a server, the
callback is used to decide whether a user is permitted to log in or
not.  You tell the library of your callback function by calling
@code{gsasl_callback_set}.

Since your callback may need to access to data from other parts of
your application, there are hooks to store and retrieve application
specific pointers.  This avoid the use of global variables in your
application, which wouldn't be thread safe.  You store a pointer to
some information (opaque from the point of view of the library) by
calling @code{gsasl_callback_hook_set} and can later retrieve this
data in your callback by calling @code{gsasl_callback_hook_get}.

@include texi/callback.c.texi

@c **********************************************************
@c ******************  Property Functions  ******************
@c **********************************************************
@node Property Functions
@chapter Property Functions
@cindex Properties

@include texi/property.c.texi


@c **********************************************************
@c *****************  Session Functions  ********************
@c **********************************************************
@node Session Functions
@chapter Session Functions
@cindex SASL sessions

@include texi/xstart.c.texi
@include texi/xstep.c.texi
@include texi/xfinish.c.texi
@include texi/xcode.c.texi



@c **********************************************************
@c *******************  Utilities  **************************
@c **********************************************************
@node Utilities
@chapter Utilities

@include texi/saslprep.c.texi
@include texi/base64.c.texi
@include texi/md5pwd.c.texi
@include texi/crypto.c.texi



@c **********************************************************
@c *******************  Errors  ****************************
@c **********************************************************
@node Error Handling
@chapter Error Handling
@cindex Error Handling

Most functions in the GNU SASL Library are returning an error if they
fail.  For this reason, the application should always catch the error
condition and take appropriate measures, for example by releasing the
resources and passing the error up to the caller, or by displaying a
descriptive message to the user and cancelling the operation.

Some error values do not indicate a system error or an error in the
operation, but the result of an operation that failed properly.

@menu
* Error values::                A list of all error values used.
* Error strings::               How to get a descriptive string from a value.
@end menu

@node Error values
@section Error values

Errors are returned as an @code{int}.  Except for the OK case an
application should always use the constants instead of their numeric
value.  Applications are encouraged to use the constants even for OK
as it improves readability.  Possible values are:

@table @code
@item @code{GSASL_OK}
This value indicates success.  The value of this error is guaranteed
to always be @code{0} so you may use it in boolean constructs.

@include gsasl-api-error-labels.texi

@end table

@node Error strings
@section Error strings

@include texi/error.c.texi

@c **********************************************************
@c ***********************  Examples  ***********************
@c **********************************************************
@node Examples
@chapter Examples
@cindex Examples

This chapter contains example code which illustrate how the GNU SASL
Library can be used when writing your own application.

@menu
* Example 1::           SASL client.
* Example 2::           SASL client where server send data first.
* Example 3::           SASL client, with a choice of mechanism to use.
* Example 4::           SASL client, with callback for user info.
@end menu

@node Example 1
@section Example 1

@example
@verbatiminclude client.c
@end example

@node Example 2
@section Example 2

@example
@verbatiminclude client-serverfirst.c
@end example

@node Example 3
@section Example 3

@example
@verbatiminclude client-mech.c
@end example

@node Example 4
@section Example 4

@example
@verbatiminclude client-callback.c
@end example


@c **********************************************************
@c *******************  Acknowledgements  *******************
@c **********************************************************
@node Acknowledgements
@chapter Acknowledgements

The makefiles, manuals, etc borrowed much from Libgcrypt written by
Werner Koch.

Cryptographic functions for some SASL mechanisms uses Libgcrypt by
Werner Koch et al.  The NTLM mechanism uses Libntlm by Grant Edwards
et al, using code from Samba written by Andrew Tridgell, and now
maintained by Simon Josefsson.  The KERBEROS_V5 mechanism uses Shishi
by Simon Josefsson.  The GSSAPI mechanism uses a GSS-API
implementation, such as GSSLib by Simon Josefsson.

Gnulib is used to simplify portability.

This manual borrows text from the SASL specification.

@c **********************************************************
@c ********************  Invoking gsasl  ********************
@c **********************************************************
@node Invoking gsasl
@chapter Invoking gsasl

@pindex gsasl
@cindex invoking @command{gsasl}
@cindex command line

@majorheading Name

GNU SASL (gsasl) -- Command line interface to libgsasl.

@majorheading Description
@code{gsasl} is the main program of GNU SASL.

This section only lists the commands and options available.

Mandatory or optional arguments to long options are also mandatory or
optional for any corresponding short options.

@majorheading Commands
@code{gsasl} recognizes these commands:

@verbatim
  -c, --client               Act as client (the default).
      --client-mechanisms    Write name of supported client mechanisms
                             separated by space to stdout.
  -s, --server               Act as server.
      --server-mechanisms    Write name of supported server mechanisms
                             separated by space to stdout.
@end verbatim

@majorheading Network Options

Normally the SASL negotiation is performed on the terminal, with
reading from stdin and writing to stdout.  It is also possible to
perform the negotiation with a server over a TCP network connection.

@verbatim
      --connect=HOSTNAME[:SERVICE]
                             Connect to TCP server and negotiate on stream
                             instead of stdin/stdout. SERVICE is the protocol
                             service, or an integer denoting the port, and
                             defaults to 143 (imap) if not specified. Also sets
                             the --hostname default.
@end verbatim

@majorheading Miscellaneous Options:

These parameters affect overall behaviour.

@verbatim
  -d, --application-data     After authentication, read data from stdin and run
                             it through the mechanism's security layer and
                             print it base64 encoded to stdout. The default is
                             to terminate after authentication.
      --imap                 Use a IMAP-like logon procedure (client only).
                             Also sets the --service default to "imap".
  -m, --mechanism=STRING     Mechanism to use.
      --no-client-first      Disallow client to send data first (client only).
@end verbatim

@majorheading SASL Mechanism Options

These options modify the behaviour of the callbacks (@pxref{Callback
Functions}) in the library.  The default is the query the user on the
terminal.

@verbatim
  -n, --anonymous-token=STRING    Token for anonymous authentication, usually
                                  mail address (ANONYMOUS only).
  -a, --authentication-id=STRING  Identity of credential owner.
  -z, --authorization-id=STRING   Identity to request service for.
      --disable-cleartext-validate
                             Disable cleartext validate hook, forcing server to
                             prompt for password.
      --enable-cram-md5-validate  Validate CRAM-MD5 challenge and response
                                  interactively.
      --hostname=STRING      Set the name of the server with the requested
                             service.
  -p, --password=STRING      Password for authentication (insecure for
                             non-testing purposes).
      --passcode=NUMBER      Passcode for authentication (SECURID only).
      --quality-of-protection=<auth | auth-int | auth-conf>
                             How application payload will be protected.  "auth"
                             means no protection, "auth-int" means integrity
                             protection, "auth-conf" means integrity and
                             confidentialiy protection.  Currently only used by
                             DIGEST-MD5, where the default is "auth-conf".
  -r, --realm=STRING         Realm. Defaults to hostname.
      --service=STRING       Set the requested service name (should be a
                             registered GSSAPI host based service name).
      --service-name=STRING  Set the generic server name in case of a
                             replicated server (DIGEST-MD5 only).
  -x, --maxbuf=NUMBER        Indicate maximum buffer size (DIGEST-MD5 only).
@end verbatim

@majorheading STARTTLS options

@verbatim
      --starttls                Force use of STARTTLS.  The default is to use
                                  STARTTLS when available.  (default=off)
      --no-starttls             Unconditionally disable STARTTLS.
                                  (default=off)
      --x509-ca-file=FILE       File containing one or more X.509 Certificate
                                  Authorities certificates in PEM format, used
                                  to verify the certificate received from the
                                  server.  If not specified, no verification of
                                  the remote server certificate will be done.
      --x509-cert-file=FILE     File containing client X.509 certificate in PEM
                                  format.  Used together with --x509-key-file
                                  to specify the certificate/key pair.
      --x509-key-file=FILE      Private key for the client X.509 certificate in
                                  PEM format.  Used together with
                                  --x509-key-file to specify the
                                  certificate/key pair.
@end verbatim

@majorheading Other Options

These are some standard parameters.

@verbatim
  -q, --quiet, --silent      Don't produce any diagnostic output.
  -v, --verbose              Produce verbose output.

  -?, --help                 Give this help list
      --usage                Give a short usage message
  -V, --version              Print program version
@end verbatim

@c **********************************************************
@c *******************  Appendices  *************************
@c **********************************************************

@node Protocol Clarifications
@appendix Protocol Clarifications

This appendix contain clarification to various SASL specification that
we felt were necessary to include, if for nothing else it may serve as
a guide for other implementors that worry about the same issues.

@menu
* Use of SASLprep in CRAM-MD5::
* Use of SASLprep in LOGIN::
@end menu

@node Use of SASLprep in CRAM-MD5
@section Use of SASLprep in CRAM-MD5

The specification, as of @file{draft-ietf-sasl-crammd5-04.txt}, is
silent on whether a SASL server implementation applying
@acronym{SASLprep} on a password received from an external, non-SASL
specific database (i.e., the passwords are not stored in
@acronym{SASLprep} form in the database), should set or clear the
AllowUnassigned bit.  The motivation for the AU-bit in
@acronym{StringPrep}/@acronym{SASLprep} is for stored vs query
strings.  It could be argued that in this situation the server can
treat the external password either as a stored string (from a
database) or as a query (the server uses the string as a query into
the fixed HMAC-MD5 hash).

The specification is also unclear on whether clients should set or
clear the AllowUnassigned flag.

In the server, GNU SASL apply @acronym{SASLprep} to the password with
the AllowUnassigned bit cleared.

@node Use of SASLprep in LOGIN
@section Use of SASLprep in LOGIN

The non-standard mechanism LOGIN presumably does not support
non-ASCII.  We suggest that the client should send unprepared UTF-8
and that the server apply SASLprep with the AllowUnassigned bit
cleared on the received username and password.

@c **********************************************************
@c *******************  Old Functions  **********************
@c **********************************************************
@node Old Functions
@appendix Old Functions
@cindex Deprecated functions
@cindex Obsolete functions

As GNU SASL is still under heavy development, some API functions have
been found to be less useful.  Those old API functions will be
supported during a transition period.  Refer to the NEWS file to find
out since when a function has been deprecated.

@include texi/obsolete.c.texi

@section Obsolete callback function prototypes

@deftypefn Prototype int (*Gsasl_client_callback_anonymous) (Gsasl_session_ctx * @var{ctx}, char * @var{out}, size_t * @var{outlen})

@var{ctx}:  libgsasl handle.

@var{out}:  output array with client token.

@var{outlen}:  on input the maximum size of the output array, on output
contains the actual size of the output array.

Type of callback function the application implements.  It should
populate the output array with some input from the user and set the
output array length, and return @code{GSASL_OK}, or fail with an error
code.

If OUT is NULL, the function should only populate the output length
field with the length, and return GSASL_OK.  This usage may be used by
the caller to allocate the proper buffer size.

@end deftypefn

@deftypefn Prototype int (*Gsasl_server_callback_anonymous) (Gsasl_session_ctx * @var{ctx}, const char * @var{token})

@var{ctx}:  libgsasl handle.

@var{ctx}:  output array with client token.

@var{ctx}:  on input the maximum size of the output array, on output
contains the actual size of the output array.  If OUT is

Type of callback function the application implements.  It should
return @code{GSASL_OK} if user should be permitted anonymous access,
otherwise @code{GSASL_AUTHENTICATION_ERROR}.

@end deftypefn

@include gsasl-callback-authentication.texi
@include gsasl-callback-authorization.texi
@include gsasl-callback-client-service.texi
@include gsasl-callback-cram-md5.texi
@include gsasl-callback-digest-md5.texi

@deftypefn Prototype int (*Gsasl_server_callback_external) (Gsasl_session_ctx * @var{ctx})

@var{ctx}:  libgsasl handle.

Type of callback function the application implements.  It should
return @code{GSASL_OK} if user is authenticated by out of band means,
otherwise @code{GSASL_AUTHENTICATION_ERROR}.

@end deftypefn

@include gsasl-callback-gssapi.texi
@include gsasl-callback-passcode.texi
@include gsasl-callback-password.texi
@include gsasl-callback-retrieve.texi
@include gsasl-callback-securid.texi
@include gsasl-callback-server-service.texi
@include gsasl-callback-validate.texi

@node Copying This Manual
@appendix Copying This Manual

@menu
* GNU Free Documentation License::  License for copying this manual.
@end menu

@include fdl.texi

@node Concept Index
@unnumbered Concept Index

@printindex cp

@node Function and Data Index
@unnumbered Function and Data Index

@printindex fn

@bye