credential.h

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