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Taikun OCP Guide

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Using external authentication with Keystone

When Keystone is executed in a web server like Apache HTTPD, it is
possible to have the web server also handle authentication. This enables
support for additional methods of authentication that are not provided
by the identity store backend and the authentication plugins that
Keystone supports.

Having the web server handle authentication is not exclusive, and
both Keystone and the web server can provide different methods of
authentication at the same time. For example, the web server can provide
support for X.509 or Kerberos authentication, while Keystone provides
support for password authentication (with SQL or an identity store as
the backend).

When the web server authenticates a user, it sets environment
variables, usually REMOTE_USER, which can be used in the
underlying application. Keystone can be configured to use these
environment variables to determine the identity of the user.

Configuration

In order to activate the external authentication mechanism for
Identity API v3, the external method must be in the list of
enabled authentication methods. By default it is enabled, so if you
don’t want to use external authentication, remove it from the
methods option in the auth section.

To configure the plugin that should be used set the
external option again in the auth section.
There are two external authentication method plugins provided by
Keystone:

  • DefaultDomain: This plugin won’t take into account the
    domain information that the external authentication method may pass down
    to Keystone and will always use the configured default domain. The
    REMOTE_USER variable is the username. This is the default
    if no plugin is given.
  • Domain: This plugin expects that the
    REMOTE_DOMAIN variable contains the domain for the user. If
    this variable is not present, the configured default domain will be
    used. The REMOTE_USER variable is the username.

Caution

You should disable the external auth method if you are currently
using federation. External auth and federation both use the
REMOTE_USER variable. Since both the mapped and external
plugin are being invoked to validate attributes in the request
environment, it can cause conflicts.

For example, imagine there are two distinct users with the same
username foo, one in the Default domain while the other is in the BAR domain. The external Federation modules
(i.e. mod_shib) sets the REMOTE_USER attribute to foo. The external auth module also tries to set
the REMOTE_USER attribute to foo for the Default domain. The federated mapping engine
maps the incoming identity to foo in the
BAR domain. This results in user_id
conflict since both are using different user_ids to set foo in the Default domain and the BAR domain.

To disable this, simply remove external from the methods option in `keystone.conf`:

methods = external,password,token,oauth1

Using HTTPD authentication

Web servers like Apache HTTP support many methods of authentication.
Keystone can profit from this feature and let the authentication be done
in the web server, that will pass down the authenticated user to
Keystone using the REMOTE_USER environment variable. This
user must exist in advance in the identity backend to get a token from
the controller.

To use this method, Keystone should be running on HTTPD.

X.509 example

The following snippet for the Apache conf will authenticate the user
based on a valid X.509 certificate from a known CA:

<VirtualHost _default_:5000>
    SSLEngine on
    SSLCertificateFile    /etc/ssl/certs/ssl.cert
    SSLCertificateKeyFile /etc/ssl/private/ssl.key

    SSLCACertificatePath /etc/ssl/allowed_cas
    SSLCARevocationPath  /etc/ssl/allowed_cas
    SSLUserName          SSL_CLIENT_S_DN_CN
    SSLVerifyClient      require
    SSLVerifyDepth       10

    (...)
</VirtualHost>

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