mirror of
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Git authentication with OAuth access token is supported by every popular
Git host including GitHub, GitLab and BitBucket [1][2][3]. Credential
helpers Git Credential Manager (GCM) and git-credential-oauth generate
OAuth credentials [4][5]. Following RFC 6749, the application prints a
link for the user to authorize access in browser. A loopback redirect
communicates the response including access token to the application.
For security, RFC 6749 recommends that OAuth response also includes
expiry date and refresh token [6]. After expiry, applications can use
the refresh token to generate a new access token without user
reauthorization in browser. GitLab and BitBucket set the expiry at two
hours [2][3]. (GitHub doesn't populate expiry or refresh token.)
However the Git credential protocol has no attribute to store the OAuth
refresh token (unrecognised attributes are silently discarded). This
means that the user has to regularly reauthorize the helper in browser.
On a browserless system, this is particularly intrusive, requiring a
second device.
Introduce a new attribute oauth_refresh_token. This is especially
useful when a storage helper and a read-only OAuth helper are configured
together. Recall that `credential fill` calls each helper until it has a
non-expired password.
```
[credential]
helper = storage # eg. cache or osxkeychain
helper = oauth
```
The OAuth helper can use the stored refresh token forwarded by
`credential fill` to generate a fresh access token without opening the
browser. See
https://github.com/hickford/git-credential-oauth/pull/3/files
for an implementation tested with this patch.
Add support for the new attribute to credential-cache. Eventually, I
hope to see support in other popular storage helpers.
Alternatives considered: ask helpers to store all unrecognised
attributes. This seems excessively complex for no obvious gain.
Helpers would also need extra information to distinguish between
confidential and non-confidential attributes.
Workarounds: GCM abuses the helper get/store/erase contract to store the
refresh token during credential *get* as the password for a fictitious
host [7] (I wrote this hack). This workaround is only feasible for a
monolithic helper with its own storage.
[1] https://github.blog/2012-09-21-easier-builds-and-deployments-using-git-over-https-and-oauth/
[2] https://docs.gitlab.com/ee/api/oauth2.html#access-git-over-https-with-access-token
[3] https://support.atlassian.com/bitbucket-cloud/docs/use-oauth-on-bitbucket-cloud/#Cloning-a-repository-with-an-access-token
[4] https://github.com/GitCredentialManager/git-credential-manager
[5] https://github.com/hickford/git-credential-oauth
[6] https://datatracker.ietf.org/doc/html/rfc6749#section-5.1
[7] 66b94e489a/src/shared/GitLab/GitLabHostProvider.cs (L207)
Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
180 lines
6.4 KiB
Plaintext
180 lines
6.4 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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`oauth_refresh_token`::
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An OAuth refresh token may accompany a password that is an OAuth access
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token. Helpers must treat this attribute as confidential like the password
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attribute. Git itself has no special behaviour for this attribute.
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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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