keystone/doc/source/external-auth.rst

Using external authentication with Keystone

When Keystone is executed in HTTPD <apache-httpd> it is possible to use external authentication methods different from the authentication provided by the identity store backend. For example, this makes possible to use a SQL identity backend together with X.509 authentication, Kerberos, etc. instead of using the username/password combination.

Using HTTPD authentication

Webservers like Apache HTTP support many methods of authentication. Keystone can profit from this feature and let the authentication be done in the webserver, 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 so as to get a token from the controller.

To use this method, Keystone should be running on HTTPD <apache-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>

Developing a WSGI middleware for authentication

In addition to the method described above, it is possible to implement other custom authentication mechanisms using the REMOTE_USER WSGI environment variable.

Attention

Please note that even if it is possible to develop a custom authentication module, it is preferable to use the modules in the HTTPD server. Such authentication modules in webservers like Apache have normally undergone years of development and use in production systems and are actively maintained upstream. Developing a custom authentication module that implements the same authentication as an existing Apache module likely introduces a higher security risk.

If you find you must implement a custom authentication mechanism, you will need to develop a custom WSGI middleware pipeline component. This middleware should set the environment variable REMOTE_USER to the authenticated username. Keystone then will assume that the user has been already authenticated upstream and will not try to authenticate it. However, as with HTTPD authentication, the user must exist in advance in the identity backend so that a proper token can be issued.

Your code should set the REMOTE_USER if the user is properly authenticated, following the semantics below:

class MyMiddlewareAuth(wsgi.Middleware):
    def __init__(self, *args, **kwargs):
        super(MyMiddlewareAuth, self).__init__(*args, **kwargs)

    def process_request(self, request):
        if request.environ.get('REMOTE_USER', None) is not None:
            # Assume that it is authenticated upstream
            return self.application

        if not self.is_auth_applicable(request):
            # Not applicable
            return self.application

        username = self.do_auth(request):
        if username is not None:
            # User is authenticated
            request.environ['REMOTE_USER'] = username
        else:
            # User is not authenticated
            raise exception.Unauthorized("Invalid user")

Pipeline configuration

Once you have your WSGI middleware component developed you have to add it to your pipeline. The first step is to add the middleware to your configuration file. Assuming that your middleware module is keystone.middleware.MyMiddlewareAuth, you can configure it in your keystone.conf as:

[filter:my_auth]
paste.filter_factory = keystone.middleware.MyMiddlewareAuth.factory

The second step is to add your middleware to the pipeline. The exact place where you should place it will depend on your code (i.e. if you need for example that the request body is converted from JSON before perform the authentication you should place it after the json_body filter) but it should be set before the public_service (for the public_api pipeline) or admin_service (for the admin_api pipeline), since they consume authentication.

For example, if the original pipeline looks like this:

[pipeline:public_api]
pipeline = stats_monitoring url_normalize token_auth admin_token_auth xml_body json_body debug ec2_extension user_crud_extension public_service

Your modified pipeline might then look like this:

[pipeline:public_api]
pipeline = stats_monitoring url_normalize token_auth admin_token_auth xml_body json_body my_auth debug ec2_extension user_crud_extension public_service