credential.h

   1 #ifndef CREDENTIAL_H
   2 #define CREDENTIAL_H
   3
   4 #include "string-list.h"
   5 #include "strvec.h"
   6
   7 /**
   8  * The credentials API provides an abstracted way of gathering username and
   9  * password credentials from the user.
  10  *
  11  * Typical setup
  12  * -------------
  13  *
  14  * ------------
  15  * +-----------------------+
  16  * | Git code (C)          |--- to server requiring --->
  17  * |                       |        authentication
  18  * |.......................|
  19  * | C credential API      |--- prompt ---> User
  20  * +-----------------------+
  21  *      ^      |
  22  *      | pipe |
  23  *      |      v
  24  * +-----------------------+
  25  * | Git credential helper |
  26  * +-----------------------+
  27  * ------------
  28  *
  29  * The Git code (typically a remote-helper) will call the C API to obtain
  30  * credential data like a login/password pair (credential_fill). The
  31  * API will itself call a remote helper (e.g. "git credential-cache" or
  32  * "git credential-store") that may retrieve credential data from a
  33  * store. If the credential helper cannot find the information, the C API
  34  * will prompt the user. Then, the caller of the API takes care of
  35  * contacting the server, and does the actual authentication.
  36  *
  37  * C API
  38  * -----
  39  *
  40  * The credential C API is meant to be called by Git code which needs to
  41  * acquire or store a credential. It is centered around an object
  42  * representing a single credential and provides three basic operations:
  43  * fill (acquire credentials by calling helpers and/or prompting the user),
  44  * approve (mark a credential as successfully used so that it can be stored
  45  * for later use), and reject (mark a credential as unsuccessful so that it
  46  * can be erased from any persistent storage).
  47  *
  48  * Example
  49  * ~~~~~~~
  50  *
  51  * The example below shows how the functions of the credential API could be
  52  * used to login to a fictitious "foo" service on a remote host:
  53  *
  54  * -----------------------------------------------------------------------
  55  * int foo_login(struct foo_connection *f)
  56  * {
  57  *      int status;
  58  *      // Create a credential with some context; we don't yet know the
  59  *      // username or password.
  60  *
  61  * struct credential c = CREDENTIAL_INIT;
  62  * c.protocol = xstrdup("foo");
  63  * c.host = xstrdup(f->hostname);
  64  *
  65  * // Fill in the username and password fields by contacting
  66  * // helpers and/or asking the user. The function will die if it
  67  * // fails.
  68  * credential_fill(&c);
  69  *
  70  * // Otherwise, we have a username and password. Try to use it.
  71  *
  72  * status = send_foo_login(f, c.username, c.password);
  73  * switch (status) {
  74  * case FOO_OK:
  75  * // It worked. Store the credential for later use.
  76  * credential_accept(&c);
  77  * break;
  78  * case FOO_BAD_LOGIN:
  79  * // Erase the credential from storage so we don't try it again.
  80  * credential_reject(&c);
  81  * break;
  82  * default:
  83  * // Some other error occurred. We don't know if the
  84  * // credential is good or bad, so report nothing to the
  85  * // credential subsystem.
  86  * }
  87  *
  88  * // Free any associated resources.
  89  * credential_clear(&c);
  90  *
  91  * return status;
  92  * }
  93  * -----------------------------------------------------------------------
  94  */
  95
  96
  97 /**
  98  * This struct represents a single username/password combination
  99  * along with any associated context. All string fields should be
 100  * heap-allocated (or NULL if they are not known or not applicable).
 101  * The meaning of the individual context fields is the same as
 102  * their counterparts in the helper protocol.
 103  *
 104  * This struct should always be initialized with `CREDENTIAL_INIT` or
 105  * `credential_init`.
 106  */
 107 struct credential {
 108
 109         /**
 110          * A `string_list` of helpers. Each string specifies an external
 111          * helper which will be run, in order, to either acquire or store
 112          * credentials. This list is filled-in by the API functions
 113          * according to the corresponding configuration variables before
 114          * consulting helpers, so there usually is no need for a caller to
 115          * modify the helpers field at all.
 116          */
 117         struct string_list helpers;
 118
 119         /**
 120          * A `strvec` of WWW-Authenticate header values. Each string
 121          * is the value of a WWW-Authenticate header in an HTTP response,
 122          * in the order they were received in the response.
 123          */
 124         struct strvec wwwauth_headers;
 125
 126         /**
 127          * Internal use only. Keeps track of if we previously matched against a
 128          * WWW-Authenticate header line in order to re-fold future continuation
 129          * lines into one value.
 130          */
 131         unsigned header_is_last_match:1;
 132
 133         unsigned approved:1,
 134                  configured:1,
 135                  quit:1,
 136                  use_http_path:1,
 137                  username_from_proto:1;
 138
 139         char *username;
 140         char *password;
 141         char *protocol;
 142         char *host;
 143         char *path;
 144         timestamp_t password_expiry_utc;
 145 };
 146
 147 #define CREDENTIAL_INIT { \
 148         .helpers = STRING_LIST_INIT_DUP, \
 149         .password_expiry_utc = TIME_MAX, \
 150         .wwwauth_headers = STRVEC_INIT, \
 151 }
 152
 153 /* Initialize a credential structure, setting all fields to empty. */
 154 void credential_init(struct credential *);
 155
 156 /**
 157  * Free any resources associated with the credential structure, returning
 158  * it to a pristine initialized state.
 159  */
 160 void credential_clear(struct credential *);
 161
 162 /**
 163  * Instruct the credential subsystem to fill the username and
 164  * password fields of the passed credential struct by first
 165  * consulting helpers, then asking the user. After this function
 166  * returns, the username and password fields of the credential are
 167  * guaranteed to be non-NULL. If an error occurs, the function will
 168  * die().
 169  */
 170 void credential_fill(struct credential *);
 171
 172 /**
 173  * Inform the credential subsystem that the provided credentials
 174  * were successfully used for authentication.  This will cause the
 175  * credential subsystem to notify any helpers of the approval, so
 176  * that they may store the result to be used again.  Any errors
 177  * from helpers are ignored.
 178  */
 179 void credential_approve(struct credential *);
 180
 181 /**
 182  * Inform the credential subsystem that the provided credentials
 183  * have been rejected. This will cause the credential subsystem to
 184  * notify any helpers of the rejection (which allows them, for
 185  * example, to purge the invalid credentials from storage). It
 186  * will also free() the username and password fields of the
 187  * credential and set them to NULL (readying the credential for
 188  * another call to `credential_fill`). Any errors from helpers are
 189  * ignored.
 190  */
 191 void credential_reject(struct credential *);
 192
 193 int credential_read(struct credential *, FILE *);
 194 void credential_write(const struct credential *, FILE *);
 195
 196 /*
 197  * Parse a url into a credential struct, replacing any existing contents.
 198  *
 199  * If the url can't be parsed (e.g., a missing "proto://" component), the
 200  * resulting credential will be empty and the function will return an
 201  * error (even in the "gently" form).
 202  *
 203  * If we encounter a component which cannot be represented as a credential
 204  * value (e.g., because it contains a newline), the "gently" form will return
 205  * an error but leave the broken state in the credential object for further
 206  * examination.  The non-gentle form will issue a warning to stderr and return
 207  * an empty credential.
 208  */
 209 void credential_from_url(struct credential *, const char *url);
 210 int credential_from_url_gently(struct credential *, const char *url, int quiet);
 211
 212 int credential_match(const struct credential *want,
 213                      const struct credential *have);
 214
 215 #endif /* CREDENTIAL_H */