cc4f2eb828
The details of how credential helpers can be called or implemented were
originally covered in Documentation/technical/. Those are topics that
end users might care about (and we even referenced them in the
credentials manpage), but those docs typically don't ship as part of the
end user documentation, making them less useful.
This situation got slightly worse recently in f3b9055624 (credential:
move doc to credential.h, 2019-11-17), where we moved them into the C
header file, making them even harder to find.
So let's move put this information into the gitcredentials(7)
documentation, which is meant to describe the overall concepts of our
credential handling. This was already pointing to the API docs for these
concepts, so we can just include it inline instead.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
281 lines
9.8 KiB
Plaintext
281 lines
9.8 KiB
Plaintext
gitcredentials(7)
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=================
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NAME
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----
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gitcredentials - providing usernames and passwords to Git
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SYNOPSIS
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--------
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------------------
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git config credential.https://example.com.username myusername
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git config credential.helper "$helper $options"
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------------------
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DESCRIPTION
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-----------
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Git will sometimes need credentials from the user in order to perform
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operations; for example, it may need to ask for a username and password
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in order to access a remote repository over HTTP. This manual describes
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the mechanisms Git uses to request these credentials, as well as some
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features to avoid inputting these credentials repeatedly.
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REQUESTING CREDENTIALS
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----------------------
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Without any credential helpers defined, Git will try the following
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strategies to ask the user for usernames and passwords:
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1. If the `GIT_ASKPASS` environment variable is set, the program
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specified by the variable is invoked. A suitable prompt is provided
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to the program on the command line, and the user's input is read
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from its standard output.
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2. Otherwise, if the `core.askPass` configuration variable is set, its
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value is used as above.
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3. Otherwise, if the `SSH_ASKPASS` environment variable is set, its
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value is used as above.
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4. Otherwise, the user is prompted on the terminal.
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AVOIDING REPETITION
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-------------------
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It can be cumbersome to input the same credentials over and over. Git
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provides two methods to reduce this annoyance:
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1. Static configuration of usernames for a given authentication context.
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2. Credential helpers to cache or store passwords, or to interact with
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a system password wallet or keychain.
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The first is simple and appropriate if you do not have secure storage available
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for a password. It is generally configured by adding this to your config:
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---------------------------------------
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[credential "https://example.com"]
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username = me
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---------------------------------------
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Credential helpers, on the other hand, are external programs from which Git can
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request both usernames and passwords; they typically interface with secure
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storage provided by the OS or other programs.
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To use a helper, you must first select one to use. Git currently
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includes the following helpers:
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cache::
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Cache credentials in memory for a short period of time. See
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linkgit:git-credential-cache[1] for details.
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store::
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Store credentials indefinitely on disk. See
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linkgit:git-credential-store[1] for details.
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You may also have third-party helpers installed; search for
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`credential-*` in the output of `git help -a`, and consult the
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documentation of individual helpers. Once you have selected a helper,
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you can tell Git to use it by putting its name into the
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credential.helper variable.
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1. Find a helper.
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+
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-------------------------------------------
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$ git help -a | grep credential-
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credential-foo
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-------------------------------------------
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2. Read its description.
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+
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-------------------------------------------
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$ git help credential-foo
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-------------------------------------------
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3. Tell Git to use it.
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+
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-------------------------------------------
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$ git config --global credential.helper foo
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-------------------------------------------
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CREDENTIAL CONTEXTS
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-------------------
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Git considers each credential to have a context defined by a URL. This context
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is used to look up context-specific configuration, and is passed to any
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helpers, which may use it as an index into secure storage.
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For instance, imagine we are accessing `https://example.com/foo.git`. When Git
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looks into a config file to see if a section matches this context, it will
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consider the two a match if the context is a more-specific subset of the
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pattern in the config file. For example, if you have this in your config file:
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--------------------------------------
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[credential "https://example.com"]
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username = foo
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--------------------------------------
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then we will match: both protocols are the same, both hosts are the same, and
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the "pattern" URL does not care about the path component at all. However, this
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context would not match:
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--------------------------------------
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[credential "https://kernel.org"]
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username = foo
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--------------------------------------
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because the hostnames differ. Nor would it match `foo.example.com`; Git
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compares hostnames exactly, without considering whether two hosts are part of
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the same domain. Likewise, a config entry for `http://example.com` would not
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match: Git compares the protocols exactly.
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If the "pattern" URL does include a path component, then this too must match
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exactly: the context `https://example.com/bar/baz.git` will match a config
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entry for `https://example.com/bar/baz.git` (in addition to matching the config
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entry for `https://example.com`) but will not match a config entry for
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`https://example.com/bar`.
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CONFIGURATION OPTIONS
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---------------------
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Options for a credential context can be configured either in
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`credential.*` (which applies to all credentials), or
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`credential.<url>.*`, where <url> matches the context as described
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above.
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The following options are available in either location:
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helper::
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The name of an external credential helper, and any associated options.
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If the helper name is not an absolute path, then the string `git
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credential-` is prepended. The resulting string is executed by the
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shell (so, for example, setting this to `foo --option=bar` will execute
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`git credential-foo --option=bar` via the shell. See the manual of
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specific helpers for examples of their use.
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+
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If there are multiple instances of the `credential.helper` configuration
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variable, each helper will be tried in turn, and may provide a username,
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password, or nothing. Once Git has acquired both a username and a
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password, no more helpers will be tried.
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+
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If `credential.helper` is configured to the empty string, this resets
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the helper list to empty (so you may override a helper set by a
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lower-priority config file by configuring the empty-string helper,
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followed by whatever set of helpers you would like).
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username::
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A default username, if one is not provided in the URL.
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useHttpPath::
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By default, Git does not consider the "path" component of an http URL
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to be worth matching via external helpers. This means that a credential
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stored for `https://example.com/foo.git` will also be used for
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`https://example.com/bar.git`. If you do want to distinguish these
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cases, set this option to `true`.
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CUSTOM HELPERS
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--------------
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You can write your own custom helpers to interface with any system in
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which you keep credentials.
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Credential helpers are programs executed by Git to fetch or save
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credentials from and to long-term storage (where "long-term" is simply
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longer than a single Git process; e.g., credentials may be stored
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in-memory for a few minutes, or indefinitely on disk).
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Each helper is specified by a single string in the configuration
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variable `credential.helper` (and others, see linkgit:git-config[1]).
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The string is transformed by Git into a command to be executed using
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these rules:
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1. If the helper string begins with "!", it is considered a shell
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snippet, and everything after the "!" becomes the command.
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2. Otherwise, if the helper string begins with an absolute path, the
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verbatim helper string becomes the command.
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3. Otherwise, the string "git credential-" is prepended to the helper
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string, and the result becomes the command.
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The resulting command then has an "operation" argument appended to it
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(see below for details), and the result is executed by the shell.
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Here are some example specifications:
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----------------------------------------------------
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# run "git credential-foo"
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foo
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# same as above, but pass an argument to the helper
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foo --bar=baz
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# the arguments are parsed by the shell, so use shell
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# quoting if necessary
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foo --bar="whitespace arg"
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# you can also use an absolute path, which will not use the git wrapper
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/path/to/my/helper --with-arguments
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# or you can specify your own shell snippet
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!f() { echo "password=`cat $HOME/.secret`"; }; f
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----------------------------------------------------
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Generally speaking, rule (3) above is the simplest for users to specify.
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Authors of credential helpers should make an effort to assist their
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users by naming their program "git-credential-$NAME", and putting it in
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the `$PATH` or `$GIT_EXEC_PATH` during installation, which will allow a
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user to enable it with `git config credential.helper $NAME`.
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When a helper is executed, it will have one "operation" argument
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appended to its command line, which is one of:
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`get`::
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Return a matching credential, if any exists.
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`store`::
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Store the credential, if applicable to the helper.
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`erase`::
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Remove a matching credential, if any, from the helper's storage.
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The details of the credential will be provided on the helper's stdin
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stream. The exact format is the same as the input/output format of the
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`git credential` plumbing command (see the section `INPUT/OUTPUT
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FORMAT` in linkgit:git-credential[1] for a detailed specification).
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For a `get` operation, the helper should produce a list of attributes on
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stdout in the same format (see linkgit:git-credential[1] for common
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attributes). A helper is free to produce a subset, or even no values at
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all if it has nothing useful to provide. Any provided attributes will
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overwrite those already known about by Git. If a helper outputs a
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`quit` attribute with a value of `true` or `1`, no further helpers will
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be consulted, nor will the user be prompted (if no credential has been
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provided, the operation will then fail).
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For a `store` or `erase` operation, the helper's output is ignored.
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If it fails to perform the requested operation, it may complain to
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stderr to inform the user. If it does not support the requested
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operation (e.g., a read-only store), it should silently ignore the
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request.
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If a helper receives any other operation, it should silently ignore the
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request. This leaves room for future operations to be added (older
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helpers will just ignore the new requests).
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GIT
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---
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Part of the linkgit:git[1] suite
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