git-credential.adoc

git-credential(1)
=================

NAME
----
git-credential - Retrieve and store user credentials

SYNOPSIS
--------
------------------
'git credential' (fill|approve|reject|capability)
------------------

DESCRIPTION
-----------

Git has an internal interface for storing and retrieving credentials
from system-specific helpers, as well as prompting the user for
usernames and passwords. The git-credential command exposes this
interface to scripts which may want to retrieve, store, or prompt for
credentials in the same manner as Git. The design of this scriptable
interface models the internal C API; see credential.h for more
background on the concepts.

git-credential takes an "action" option on the command-line (one of
`fill`, `approve`, or `reject`) and reads a credential description
on stdin (see <<IOFMT,INPUT/OUTPUT FORMAT>>).

If the action is `fill`, git-credential will attempt to add "username"
and "password" attributes to the description by reading config files,
by contacting any configured credential helpers, or by prompting the
user. The username and password attributes of the credential
description are then printed to stdout together with the attributes
already provided.

If the action is `approve`, git-credential will send the description
to any configured credential helpers, which may store the credential
for later use.

If the action is `reject`, git-credential will send the description to
any configured credential helpers, which may erase any stored
credentials matching the description.

If the action is `capability`, git-credential will announce any capabilities
it supports to standard output.

If the action is `approve` or `reject`, no output should be emitted.

TYPICAL USE OF GIT CREDENTIAL
-----------------------------

An application using git-credential will typically use `git
credential` following these steps:

  1. Generate a credential description based on the context.
+
For example, if we want a password for
`https://example.com/foo.git`, we might generate the following
credential description (don't forget the blank line at the end; it
tells `git credential` that the application finished feeding all the
information it has):

	 protocol=https
	 host=example.com
	 path=foo.git

  2. Ask git-credential to give us a username and password for this
     description. This is done by running `git credential fill`,
     feeding the description from step (1) to its standard input. The complete
     credential description (including the credential per se, i.e. the
     login and password) will be produced on standard output, like:

	protocol=https
	host=example.com
	username=bob
	password=secr3t
+
In most cases, this means the attributes given in the input will be
repeated in the output, but Git may also modify the credential
description, for example by removing the `path` attribute when the
protocol is HTTP(s) and `credential.useHttpPath` is false.
+
If the `git credential` knew about the password, this step may
not have involved the user actually typing this password (the
user may have typed a password to unlock the keychain instead,
or no user interaction was done if the keychain was already
unlocked) before it returned `password=secr3t`.

  3. Use the credential (e.g., access the URL with the username and
     password from step (2)), and see if it's accepted.

  4. Report on the success or failure of the password. If the
     credential allowed the operation to complete successfully, then
     it can be marked with an "approve" action to tell `git
     credential` to reuse it in its next invocation. If the credential
     was rejected during the operation, use the "reject" action so
     that `git credential` will ask for a new password in its next
     invocation. In either case, `git credential` should be fed with
     the credential description obtained from step (2) (which also
     contains the fields provided in step (1)).

[[IOFMT]]
INPUT/OUTPUT FORMAT
-------------------

`git credential` reads and/or writes (depending on the action used)
credential information in its standard input/output. This information
can correspond either to keys for which `git credential` will obtain
the login information (e.g. host, protocol, path), or to the actual
credential data to be obtained (username/password).

The credential is split into a set of named attributes, with one
attribute per line. Each attribute is specified by a key-value pair,
separated by an `=` (equals) sign, followed by a newline.

The key may contain any bytes except `=`, newline, or NUL. The value may
contain any bytes except newline or NUL.  A line, including the trailing
newline, may not exceed 65535 bytes in order to allow implementations to
parse efficiently.

Attributes with keys that end with C-style array brackets `[]` can have
multiple values. Each instance of a multi-valued attribute forms an
ordered list of values - the order of the repeated attributes defines
the order of the values. An empty multi-valued attribute (`key[]=\n`)
acts to clear any previous entries and reset the list.

In all cases, all bytes are treated as-is (i.e., there is no quoting,
and one cannot transmit a value with newline or NUL in it). The list of
attributes is terminated by a blank line or end-of-file.

Git understands the following attributes:

`protocol`::

	The protocol over which the credential will be used (e.g.,
	`https`).

`host`::

	The remote hostname for a network credential.  This includes
	the port number if one was specified (e.g., "example.com:8088").

`path`::

	The path with which the credential will be used. E.g., for
	accessing a remote https repository, this will be the
	repository's path on the server.

`username`::

	The credential's username, if we already have one (e.g., from a
	URL, the configuration, the user, or from a previously run helper).

`password`::

	The credential's password, if we are asking it to be stored.

`password_expiry_utc`::

	Generated passwords such as an OAuth access token may have an expiry date.
	When reading credentials from helpers, `git credential fill` ignores expired
	passwords. Represented as Unix time UTC, seconds since 1970.

`oauth_refresh_token`::

	An OAuth refresh token may accompany a password that is an OAuth access
	token. Helpers must treat this attribute as confidential like the password
	attribute. Git itself has no special behaviour for this attribute.

`url`::

	When this special attribute is read by `git credential`, the
	value is parsed as a URL and treated as if its constituent parts
	were read (e.g., `url=https://example.com` would behave as if
	`protocol=https` and `host=example.com` had been provided). This
	can help callers avoid parsing URLs themselves.
+
Note that specifying a protocol is mandatory and if the URL
doesn't specify a hostname (e.g., "cert:///path/to/file") the
credential will contain a hostname attribute whose value is an
empty string.
+
Components which are missing from the URL (e.g., there is no
username in the example above) will be left unset.

`authtype`::
	This indicates that the authentication scheme in question should be used.
	Common values for HTTP and HTTPS include `basic`, `bearer`, and `digest`,
	although the latter is insecure and should not be used.  If `credential`
	is used, this may be set to an arbitrary string suitable for the protocol in
	question (usually HTTP).
+
This value should not be sent unless the appropriate capability (see below) is
provided on input.

`credential`::
	The pre-encoded credential, suitable for the protocol in question (usually
	HTTP).  If this key is sent, `authtype` is mandatory, and `username` and
	`password` are not used.  For HTTP, Git concatenates the `authtype` value and
	this value with a single space to determine the `Authorization` header.
+
This value should not be sent unless the appropriate capability (see below) is
provided on input.

`ephemeral`::
	This boolean value indicates, if true, that the value in the `credential`
	field should not be saved by the credential helper because its usefulness is
	limited in time.  For example, an HTTP Digest `credential` value is computed
	using a nonce and reusing it will not result in successful authentication.
	This may also be used for situations with short duration (e.g., 24-hour)
	credentials.  The default value is false.
+
The credential helper will still be invoked with `store` or `erase` so that it
can determine whether the operation was successful.
+
This value should not be sent unless the appropriate capability (see below) is
provided on input.

`state[]`::
	This value provides an opaque state that will be passed back to this helper
	if it is called again.  Each different credential helper may specify this
	once.  The value should include a prefix unique to the credential helper and
	should ignore values that don't match its prefix.
+
This value should not be sent unless the appropriate capability (see below) is
provided on input.

`continue`::
	This is a boolean value, which, if enabled, indicates that this
	authentication is a non-final part of a multistage authentication step. This
	is common in protocols such as NTLM and Kerberos, where two rounds of client
	authentication are required, and setting this flag allows the credential
	helper to implement the multistage authentication step.  This flag should
	only be sent if a further stage is required; that is, if another round of
	authentication is expected.
+
This value should not be sent unless the appropriate capability (see below) is
provided on input.  This attribute is 'one-way' from a credential helper to
pass information to Git (or other programs invoking `git credential`).

`wwwauth[]`::

	When an HTTP response is received by Git that includes one or more
	'WWW-Authenticate' authentication headers, these will be passed by Git
	to credential helpers.
+
Each 'WWW-Authenticate' header value is passed as a multi-valued
attribute 'wwwauth[]', where the order of the attributes is the same as
they appear in the HTTP response. This attribute is 'one-way' from Git
to pass additional information to credential helpers.

`capability[]`::
	This signals that Git, or the helper, as appropriate, supports the capability
	in question.  This can be used to provide better, more specific data as part
	of the protocol.  A `capability[]` directive must precede any value depending
	on it and these directives _should_ be the first item announced in the
	protocol.
+
There are two currently supported capabilities.  The first is `authtype`, which
indicates that the `authtype`, `credential`, and `ephemeral` values are
understood.  The second is `state`, which indicates that the `state[]` and
`continue` values are understood.
+
It is not obligatory to use the additional features just because the capability
is supported, but they should not be provided without the capability.

Unrecognised attributes and capabilities are silently discarded.

[[CAPA-IOFMT]]
CAPABILITY INPUT/OUTPUT FORMAT
------------------------------

For `git credential capability`, the format is slightly different. First, a
`version 0` announcement is made to indicate the current version of the
protocol, and then each capability is announced with a line like `capability
authtype`. Credential helpers may also implement this format, again with the
`capability` argument. Additional lines may be added in the future; callers
should ignore lines which they don't understand.

Because this is a new part of the credential helper protocol, older versions of
Git, as well as some credential helpers, may not support it.  If a non-zero
exit status is received, or if the first line doesn't start with the word
`version` and a space, callers should assume that no capabilities are supported.

The intention of this format is to differentiate it from the credential output
in an unambiguous way.  It is possible to use very simple credential helpers
(e.g., inline shell scripts) which always produce identical output.  Using a
distinct format allows users to continue to use this syntax without having to
worry about correctly implementing capability advertisements or accidentally
confusing callers querying for capabilities.

GIT
---
Part of the linkgit:git[1] suite