4 The credentials API provides an abstracted way of gathering username and
5 password credentials from the user (even though credentials in the wider
6 world can take many forms, in this document the word "credential" always
7 refers to a username and password pair).
9 This document describes two interfaces: the C API that the credential
10 subsystem provides to the rest of git, and the protocol that git uses to
11 communicate with system-specific "credential helpers". If you are
12 writing git code that wants to look up or prompt for credentials, see
13 the section "C API" below. If you want to write your own helper, see
14 the section on "Credential Helpers" below.
20 +-----------------------+
21 | git code (C) |--- to server requiring --->
23 |.......................|
24 | C credential API |--- prompt ---> User
25 +-----------------------+
29 +-----------------------+
30 | git credential helper |
31 +-----------------------+
34 The git code (typically a remote-helper) will call the C API to obtain
35 credential data like a login/password pair (credential_fill). The
36 API will itself call a remote helper (e.g. "git credential-cache" or
37 "git credential-store") that may retrieve credential data from a
38 store. If the credential helper cannot find the information, the C API
39 will prompt the user. Then, the caller of the API takes care of
40 contacting the server, and does the actual authentication.
45 The credential C API is meant to be called by git code which needs to
46 acquire or store a credential. It is centered around an object
47 representing a single credential and provides three basic operations:
48 fill (acquire credentials by calling helpers and/or prompting the user),
49 approve (mark a credential as successfully used so that it can be stored
50 for later use), and reject (mark a credential as unsuccessful so that it
51 can be erased from any persistent storage).
58 This struct represents a single username/password combination
59 along with any associated context. All string fields should be
60 heap-allocated (or NULL if they are not known or not applicable).
61 The meaning of the individual context fields is the same as
62 their counterparts in the helper protocol; see the section below
63 for a description of each field.
65 The `helpers` member of the struct is a `string_list` of helpers. Each
66 string specifies an external helper which will be run, in order, to
67 either acquire or store credentials. See the section on credential
70 This struct should always be initialized with `CREDENTIAL_INIT` or
79 Initialize a credential structure, setting all fields to empty.
83 Free any resources associated with the credential structure,
84 returning it to a pristine initialized state.
88 Instruct the credential subsystem to fill the username and
89 password fields of the passed credential struct by first
90 consulting helpers, then asking the user. After this function
91 returns, the username and password fields of the credential are
92 guaranteed to be non-NULL. If an error occurs, the function will
97 Inform the credential subsystem that the provided credentials
98 have been rejected. This will cause the credential subsystem to
99 notify any helpers of the rejection (which allows them, for
100 example, to purge the invalid credentials from storage). It
101 will also free() the username and password fields of the
102 credential and set them to NULL (readying the credential for
103 another call to `credential_fill`). Any errors from helpers are
106 `credential_approve`::
108 Inform the credential subsystem that the provided credentials
109 were successfully used for authentication. This will cause the
110 credential subsystem to notify any helpers of the approval, so
111 that they may store the result to be used again. Any errors
112 from helpers are ignored.
114 `credential_from_url`::
116 Parse a URL into broken-down credential fields.
121 The example below shows how the functions of the credential API could be
122 used to login to a fictitious "foo" service on a remote host:
124 -----------------------------------------------------------------------
125 int foo_login(struct foo_connection *f)
129 * Create a credential with some context; we don't yet know the
130 * username or password.
133 struct credential c = CREDENTIAL_INIT;
134 c.protocol = xstrdup("foo");
135 c.host = xstrdup(f->hostname);
138 * Fill in the username and password fields by contacting
139 * helpers and/or asking the user. The function will die if it
145 * Otherwise, we have a username and password. Try to use it.
147 status = send_foo_login(f, c.username, c.password);
150 /* It worked. Store the credential for later use. */
151 credential_accept(&c);
154 /* Erase the credential from storage so we don't try it
156 credential_reject(&c);
160 * Some other error occured. We don't know if the
161 * credential is good or bad, so report nothing to the
162 * credential subsystem.
166 /* Free any associated resources. */
167 credential_clear(&c);
171 -----------------------------------------------------------------------
177 Credential helpers are programs executed by git to fetch or save
178 credentials from and to long-term storage (where "long-term" is simply
179 longer than a single git process; e.g., credentials may be stored
180 in-memory for a few minutes, or indefinitely on disk).
182 Each helper is specified by a single string. The string is transformed
183 by git into a command to be executed using these rules:
185 1. If the helper string begins with "!", it is considered a shell
186 snippet, and everything after the "!" becomes the command.
188 2. Otherwise, if the helper string begins with an absolute path, the
189 verbatim helper string becomes the command.
191 3. Otherwise, the string "git credential-" is prepended to the helper
192 string, and the result becomes the command.
194 The resulting command then has an "operation" argument appended to it
195 (see below for details), and the result is executed by the shell.
197 Here are some example specifications:
199 ----------------------------------------------------
200 # run "git credential-foo"
203 # same as above, but pass an argument to the helper
206 # the arguments are parsed by the shell, so use shell
207 # quoting if necessary
208 foo --bar="whitespace arg"
210 # you can also use an absolute path, which will not use the git wrapper
211 /path/to/my/helper --with-arguments
213 # or you can specify your own shell snippet
214 !f() { echo "password=`cat $HOME/.secret`"; }; f
215 ----------------------------------------------------
217 Generally speaking, rule (3) above is the simplest for users to specify.
218 Authors of credential helpers should make an effort to assist their
219 users by naming their program "git-credential-$NAME", and putting it in
220 the $PATH or $GIT_EXEC_PATH during installation, which will allow a user
221 to enable it with `git config credential.helper $NAME`.
223 When a helper is executed, it will have one "operation" argument
224 appended to its command line, which is one of:
228 Return a matching credential, if any exists.
232 Store the credential, if applicable to the helper.
236 Remove a matching credential, if any, from the helper's storage.
238 The details of the credential will be provided on the helper's stdin
239 stream. The credential is split into a set of named attributes.
240 Attributes are provided to the helper, one per line. Each attribute is
241 specified by a key-value pair, separated by an `=` (equals) sign,
242 followed by a newline. The key may contain any bytes except `=`,
243 newline, or NUL. The value may contain any bytes except newline or NUL.
244 In both cases, all bytes are treated as-is (i.e., there is no quoting,
245 and one cannot transmit a value with newline or NUL in it). The list of
246 attributes is terminated by a blank line or end-of-file.
248 Git will send the following attributes (but may not send all of
249 them for a given credential; for example, a `host` attribute makes no
250 sense when dealing with a non-network protocol):
254 The protocol over which the credential will be used (e.g.,
259 The remote hostname for a network credential.
263 The path with which the credential will be used. E.g., for
264 accessing a remote https repository, this will be the
265 repository's path on the server.
269 The credential's username, if we already have one (e.g., from a
270 URL, from the user, or from a previously run helper).
274 The credential's password, if we are asking it to be stored.
276 For a `get` operation, the helper should produce a list of attributes
277 on stdout in the same format. A helper is free to produce a subset, or
278 even no values at all if it has nothing useful to provide. Any provided
279 attributes will overwrite those already known about by git.
281 For a `store` or `erase` operation, the helper's output is ignored.
282 If it fails to perform the requested operation, it may complain to
283 stderr to inform the user. If it does not support the requested
284 operation (e.g., a read-only store), it should silently ignore the
287 If a helper receives any other operation, it should silently ignore the
288 request. This leaves room for future operations to be added (older
289 helpers will just ignore the new requests).