world can take many forms, in this document the word "credential" always
refers to a username and password pair).
+This document describes two interfaces: the C API that the credential
+subsystem provides to the rest of git, and the protocol that git uses to
+communicate with system-specific "credential helpers". If you are
+writing git code that wants to look up or prompt for credentials, see
+the section "C API" below. If you want to write your own helper, see
+the section on "Credential Helpers" below.
+
+Typical setup
+-------------
+
+------------
++-----------------------+
+| git code (C) |--- to server requiring --->
+| | authentication
+|.......................|
+| C credential API |--- prompt ---> User
++-----------------------+
+ ^ |
+ | pipe |
+ | v
++-----------------------+
+| git credential helper |
++-----------------------+
+------------
+
+The git code (typically a remote-helper) will call the C API to obtain
+credential data like a login/password pair (credential_fill). The
+API will itself call a remote helper (e.g. "git credential-cache" or
+"git credential-store") that may retrieve credential data from a
+store. If the credential helper cannot find the information, the C API
+will prompt the user. Then, the caller of the API takes care of
+contacting the server, and does the actual authentication.
+
+C API
+-----
+
+The credential C API is meant to be called by git code which needs to
+acquire or store a credential. It is centered around an object
+representing a single credential and provides three basic operations:
+fill (acquire credentials by calling helpers and/or prompting the user),
+approve (mark a credential as successfully used so that it can be stored
+for later use), and reject (mark a credential as unsuccessful so that it
+can be erased from any persistent storage).
+
Data Structures
----------------
+~~~~~~~~~~~~~~~
`struct credential`::
The `helpers` member of the struct is a `string_list` of helpers. Each
string specifies an external helper which will be run, in order, to
either acquire or store credentials. See the section on credential
-helpers below.
+helpers below. This list is filled-in by the API functions
+according to the corresponding configuration variables before
+consulting helpers, so there usually is no need for a caller to
+modify the helpers field at all.
+
This struct should always be initialized with `CREDENTIAL_INIT` or
`credential_init`.
Functions
----------
+~~~~~~~~~
`credential_init`::
Parse a URL into broken-down credential fields.
Example
--------
+~~~~~~~
The example below shows how the functions of the credential API could be
used to login to a fictitious "foo" service on a remote host:
longer than a single git process; e.g., credentials may be stored
in-memory for a few minutes, or indefinitely on disk).
-Each helper is specified by a single string. The string is transformed
-by git into a command to be executed using these rules:
+Each helper is specified by a single string in the configuration
+variable `credential.helper` (and others, see linkgit:git-config[1]).
+The string is transformed by git into a command to be executed using
+these rules:
1. If the helper string begins with "!", it is considered a shell
snippet, and everything after the "!" becomes the command.
If a helper receives any other operation, it should silently ignore the
request. This leaves room for future operations to be added (older
helpers will just ignore the new requests).
+
+See also
+--------
+
+linkgit:gitcredentials[7]
+
+linkgit:git-config[5] (See configuration variables `credential.*`)