Add authentication description doc

This is represents the current operation

Closes-Bug: #1337422

Change-Id: I8092e7723b563647e13b6e2f0b7901a16572b6c7

doc/source/authentication.rst

@@ -0,0 +1,86 @@
+==============
+Authentication
+==============
+
+OpenStackClient leverages `python-keystoneclient`_ authentication
+plugins to support a number of different authentication methods.
+
+.. _`python-keystoneclient`: http://docs.openstack.org/developer/python-keystoneclient/authentication-plugins.html
+
+Authentication Process
+----------------------
+
+The user provides some number of authentication credential options.
+If an authentication type is not provided (``--os-auth-type``), the
+authentication options are examined to determine if one of the default
+types can be used. If no match is found an error is reported and OSC exits.
+
+Note that the authentication call to the Identity service has not yet
+occurred. It is deferred until the last possible moment in order to
+reduce the number of unnecessary queries to the server, such as when further
+processing detects an invalid command.
+
+Authentication Plugins
+----------------------
+
+The Keystone client library implements the base set of plugins. Additional
+plugins may be available from the Keystone project or other sources.
+
+There are at least three authentication types that are always available:
+
+* **Password**: A project, username and password are used to identify the
+  user.  An optional domain may also be included. This is the most common
+  type and is the default any time a username is supplied.  An authentication
+  URL for the Identity service is also required. [Required: ``--os-auth-url``,
+  ``--os-project-name``, ``--os-username``; Optional: ``--os-password``]
+* **Token**: This is slightly different from the usual token authentication
+  (described below as token/endpoint) in that a token and an authentication
+  URL are supplied and the plugin retrieves a new token.
+  [Required: ``--os-auth-url``, ``--os-token``]
+* **Token/Endpoint**: This is the original token authentication (known as 'token
+  flow' in the early CLI documentation in the OpenStack wiki).  It requires
+  a token and a direct endpoint that is used in the API call.  The difference
+  from the new Token type is this token is used as-is, no call is made
+  to the Identity service from the client.  This type is most often used to
+  bootstrap a Keystone server where the token is the ``admin_token`` configured
+  in ``keystone.conf``.  It will also work with other services and a regular
+  scoped token such as one obtained from a ``token issue`` command.
+  [Required: ``--os-url``, ``--os-token``]
+* **Others**: Other authentication plugins such as SAML, Kerberos, and OAuth1.0
+  are under development and also supported. To use them, they must be selected
+  by supplying the ``--os-auth-type`` option.
+
+Detailed Process
+----------------
+
+The authentication process in OpenStackClient is all contained in and handled
+by the ``ClientManager`` object.
+
+* On import ``api.auth``:
+
+  * obtains the list of installed Keystone authentication
+    plugins from the ``keystoneclient.auth.plugin`` entry point.
+  * builds a list of authentication options from the plugins.
+
+* A new ``ClientManager`` is created and supplied with the set of options from the
+  command line and/or environment:
+
+  * If ``--os-auth-type`` is provided and is a valid and available plugin
+      it is used.
+  * If ``--os-auth-type`` is not provided an authentication plugin
+    is selected based on the existing options.  This is a short-circuit
+    evaluation, the first match wins.
+
+    * If ``--os-endpoint`` and ``--os-token`` are both present ``token_endpoint``
+      is selected
+    * If ``--os-username`` is supplied ``password`` is selected
+    * If ``--os-token`` is supplied ``token`` is selected
+    * If no selection has been made by now exit with error
+
+  * Load the selected plugin class.
+
+* When an operation that requires authentication is attempted ``ClientManager``
+  makes the actual inital request to the Identity service.
+
+  * if ``--os-auth-url`` is not supplied for any of the types except
+    Token/Endpoint, exit with an error.

doc/source/index.rst

@@ -14,6 +14,7 @@ Contents:
    releases
    commands
    plugins
+   authentication
    man/openstack
 
 Getting Started