add 'git credential' plumbing command

The credential API is in C, and not available to scripting languages.
Expose the functionalities of the API by wrapping them into a new
plumbing command "git credentials".

In other words, replace the internal "test-credential" by an official Git
command.

Most documentation writen by: Jeff King <peff@peff.net>
Signed-off-by: Pavel Volek <Pavel.Volek@ensimag.imag.fr>
Signed-off-by: Kim Thuat Nguyen <Kim-Thuat.Nguyen@ensimag.imag.fr>
Signed-off-by: Javier Roucher Iglesias <Javier.Roucher-Iglesias@ensimag.imag.fr>
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 139 insertions, 36 deletions

diff --git a/Documentation/git-credential.txt b/Documentation/git-credential.txt
new file mode 100644
index 0000000000..e70ff899d3
--- /dev/null
+++ b/Documentation/git-credential.txt
@@ -0,0 +1,136 @@
+git-credential(1)
+=================
+
+NAME
+----
+git-credential - retrieve and store user credentials
+
+SYNOPSIS
+--------
+------------------
+git credential <fill|approve|reject>
+------------------
+
+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
+link:technical/api-credentials.txt[the git credential API] 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
+credential matching the description.
+
+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
+infomation 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
+     credential will be produced on standard output, like:
+
+	username=bob
+	password=secr3t
++
+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) together with
+     the ones already 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. These information
+can correspond either to keys for which `git credential` will obtain
+the login/password information (e.g. host, protocol, path), or to the
+actual credential data to be obtained (login/password).
+
+The credential is split into a set of named attributes.
+Attributes are provided to the helper, one 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.
+In both 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 will send the following attributes (but may not send all of
+them for a given credential; for example, a `host` attribute makes no
+sense when dealing with a non-network protocol):
+
+`protocol`::
+
+	The protocol over which the credential will be used (e.g.,
+	`https`).
+
+`host`::
+
+	The remote hostname for a network credential.
+
+`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, from the user, or from a previously run helper).
+
+`password`::
+
+	The credential's password, if we are asking it to be stored.
diff --git a/Documentation/technical/api-credentials.txt b/Documentation/technical/api-credentials.txt
index adb6f0c896..5977b58e57 100644
--- a/Documentation/technical/api-credentials.txt
+++ b/Documentation/technical/api-credentials.txt
@@ -241,42 +241,9 @@ appended to its command line, which is one of:
 	Remove a matching credential, if any, from the helper's storage.
 
 The details of the credential will be provided on the helper's stdin
-stream. The credential is split into a set of named attributes.
-Attributes are provided to the helper, one 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.
-In both 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 will send the following attributes (but may not send all of
-them for a given credential; for example, a `host` attribute makes no
-sense when dealing with a non-network protocol):
-
-`protocol`::
-
-	The protocol over which the credential will be used (e.g.,
-	`https`).
-
-`host`::
-
-	The remote hostname for a network credential.
-
-`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, from the user, or from a previously run helper).
-
-`password`::
-
-	The credential's password, if we are asking it to be stored.
+stream. The exact format is the same as the input/output format of the
+`git credential` plumbing command (see the section `INPUT/OUTPUT
+FORMAT` in linkgit:git-credential[7] for a detailed specification).
 
 For a `get` operation, the helper should produce a list of attributes
 on stdout in the same format. A helper is free to produce a subset, or