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![M Hickford](/assets/img/avatar_default.png)
Some passwords have an expiry date known at generation. This may be years away for a personal access token or hours for an OAuth access token. When multiple credential helpers are configured, `credential fill` tries each helper in turn until it has a username and password, returning early. If Git authentication succeeds, `credential approve` stores the successful credential in all helpers. If authentication fails, `credential reject` erases matching credentials in all helpers. Helpers implement corresponding operations: get, store, erase. The credential protocol has no expiry attribute, so helpers cannot store expiry information. Even if a helper returned an improvised expiry attribute, git credential discards unrecognised attributes between operations and between helpers. This is a particular issue when a storage helper and a credential-generating helper are configured together: [credential] helper = storage # eg. cache or osxkeychain helper = generate # eg. oauth `credential approve` stores the generated credential in both helpers without expiry information. Later `credential fill` may return an expired credential from storage. There is no workaround, no matter how clever the second helper. The user sees authentication fail (a retry will succeed). Introduce a password expiry attribute. In `credential fill`, ignore expired passwords and continue to query subsequent helpers. In the example above, `credential fill` ignores the expired password and a fresh credential is generated. If authentication succeeds, `credential approve` replaces the expired password in storage. If authentication fails, the expired credential is erased by `credential reject`. It is unnecessary but harmless for storage helpers to self prune expired credentials. Add support for the new attribute to credential-cache. Eventually, I hope to see support in other popular storage helpers. Example usage in a credential-generating helper https://github.com/hickford/git-credential-oauth/pull/16 Signed-off-by: M Hickford <mirth.hickford@gmail.com> Reviewed-by: Calvin Wan <calvinwan@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
174 lines
6.2 KiB
Plaintext
174 lines
6.2 KiB
Plaintext
git-credential(1)
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=================
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NAME
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----
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git-credential - Retrieve and store user credentials
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SYNOPSIS
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--------
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------------------
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'git credential' (fill|approve|reject)
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------------------
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DESCRIPTION
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-----------
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Git has an internal interface for storing and retrieving credentials
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from system-specific helpers, as well as prompting the user for
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usernames and passwords. The git-credential command exposes this
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interface to scripts which may want to retrieve, store, or prompt for
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credentials in the same manner as Git. The design of this scriptable
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interface models the internal C API; see credential.h for more
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background on the concepts.
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git-credential takes an "action" option on the command-line (one of
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`fill`, `approve`, or `reject`) and reads a credential description
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on stdin (see <<IOFMT,INPUT/OUTPUT FORMAT>>).
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If the action is `fill`, git-credential will attempt to add "username"
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and "password" attributes to the description by reading config files,
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by contacting any configured credential helpers, or by prompting the
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user. The username and password attributes of the credential
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description are then printed to stdout together with the attributes
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already provided.
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If the action is `approve`, git-credential will send the description
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to any configured credential helpers, which may store the credential
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for later use.
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If the action is `reject`, git-credential will send the description to
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any configured credential helpers, which may erase any stored
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credential matching the description.
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If the action is `approve` or `reject`, no output should be emitted.
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TYPICAL USE OF GIT CREDENTIAL
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-----------------------------
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An application using git-credential will typically use `git
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credential` following these steps:
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1. Generate a credential description based on the context.
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+
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For example, if we want a password for
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`https://example.com/foo.git`, we might generate the following
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credential description (don't forget the blank line at the end; it
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tells `git credential` that the application finished feeding all the
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information it has):
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protocol=https
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host=example.com
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path=foo.git
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2. Ask git-credential to give us a username and password for this
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description. This is done by running `git credential fill`,
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feeding the description from step (1) to its standard input. The complete
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credential description (including the credential per se, i.e. the
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login and password) will be produced on standard output, like:
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protocol=https
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host=example.com
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username=bob
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password=secr3t
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+
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In most cases, this means the attributes given in the input will be
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repeated in the output, but Git may also modify the credential
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description, for example by removing the `path` attribute when the
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protocol is HTTP(s) and `credential.useHttpPath` is false.
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+
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If the `git credential` knew about the password, this step may
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not have involved the user actually typing this password (the
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user may have typed a password to unlock the keychain instead,
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or no user interaction was done if the keychain was already
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unlocked) before it returned `password=secr3t`.
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3. Use the credential (e.g., access the URL with the username and
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password from step (2)), and see if it's accepted.
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4. Report on the success or failure of the password. If the
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credential allowed the operation to complete successfully, then
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it can be marked with an "approve" action to tell `git
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credential` to reuse it in its next invocation. If the credential
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was rejected during the operation, use the "reject" action so
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that `git credential` will ask for a new password in its next
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invocation. In either case, `git credential` should be fed with
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the credential description obtained from step (2) (which also
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contain the ones provided in step (1)).
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[[IOFMT]]
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INPUT/OUTPUT FORMAT
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-------------------
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`git credential` reads and/or writes (depending on the action used)
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credential information in its standard input/output. This information
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can correspond either to keys for which `git credential` will obtain
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the login information (e.g. host, protocol, path), or to the actual
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credential data to be obtained (username/password).
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The credential is split into a set of named attributes, with one
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attribute per line. Each attribute is specified by a key-value pair,
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separated by an `=` (equals) sign, followed by a newline.
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The key may contain any bytes except `=`, newline, or NUL. The value may
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contain any bytes except newline or NUL.
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In both cases, all bytes are treated as-is (i.e., there is no quoting,
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and one cannot transmit a value with newline or NUL in it). The list of
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attributes is terminated by a blank line or end-of-file.
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Git understands the following attributes:
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`protocol`::
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The protocol over which the credential will be used (e.g.,
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`https`).
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`host`::
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The remote hostname for a network credential. This includes
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the port number if one was specified (e.g., "example.com:8088").
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`path`::
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The path with which the credential will be used. E.g., for
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accessing a remote https repository, this will be the
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repository's path on the server.
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`username`::
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The credential's username, if we already have one (e.g., from a
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URL, the configuration, the user, or from a previously run helper).
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`password`::
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The credential's password, if we are asking it to be stored.
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`password_expiry_utc`::
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Generated passwords such as an OAuth access token may have an expiry date.
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When reading credentials from helpers, `git credential fill` ignores expired
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passwords. Represented as Unix time UTC, seconds since 1970.
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`url`::
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When this special attribute is read by `git credential`, the
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value is parsed as a URL and treated as if its constituent parts
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were read (e.g., `url=https://example.com` would behave as if
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`protocol=https` and `host=example.com` had been provided). This
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can help callers avoid parsing URLs themselves.
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+
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Note that specifying a protocol is mandatory and if the URL
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doesn't specify a hostname (e.g., "cert:///path/to/file") the
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credential will contain a hostname attribute whose value is an
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empty string.
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+
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Components which are missing from the URL (e.g., there is no
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username in the example above) will be left unset.
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Unrecognised attributes are silently discarded.
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GIT
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---
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Part of the linkgit:git[1] suite
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