Adding OpenID Support

OpenID is a mechanism whereby you may delegate authentication of the user’s identity to third-parties. This allows users to use a single-sign-on service, such as their web-mail provider to authenticate at your site.

The OpenID protocol allows you to request additional information about the user, such as their email, display-name, preferred userid, etceteras. It also allows the user to deny or customize that information as it is provided to you.

There is an OpenID plugin for repoze.who which is generally configured via a who.ini file. As an example of what you can do with a custom configuration when using who.ini, let’s add the ability to use OpenID to our configuration.

Installation

We need to install the repoze.who.plugins.openid package:

easy_install repoze.who.plugins.openid

Note

You will have to use at least version 0.5.3 or above of repoze.who.plugins.openid, for this tutorial. Certain features such as the callback to create new user records on authentication are very new to the plugin.

Since we will be building on the custom who.ini mechanism, we need to be using who.ini before we start this process. If you aren’t currently using who.ini, follow through that process first.

Auto-registration on OpenID Authentication

Note

OpenIDs are cheap, do not use them for authorization by themselves. While legitimate users might be wary of tarnishing their main email address’s “good name”, an attacker can set up a server that will authenticate them in a few minutes. A user presenting an OpenID is not to be trusted based solely based on that provision of information.

If you are starting from a Quick-started project, your applications will be based around a database-based model of Users, Groups and Permissions. To minimize the impact on your application in supporting OpenID, you will normally want to enroll authenticated OpenID users as Users in your database.

The registration process must determine the level of authorization to grant an OpenID-based enrollment. Keeping in mind that OpenIDs are cheap, this should likely be about the same level of authorization as a user who has provided a (validated) email address. In our example code we don’t add the user to any permission-group.

Our registration will be done by our Metadata Provider. The Metadata Provider is responsible for providing information such as a user’s display-name or gender about an account based on the identity of the account. There is currently an SQLAlchemy Metadata provider which uses the User and Group accounts to provide Metadata, we set this up in our switch to using who.ini in our lib/auth.py module (we named it md_group_plugin there).

Here’s our new metadata provider (in lib/auth.py):

class OpenIDMetadata( object ):
    key_map = {
        # maps identity : sreg keys
        'display_name': 'fullname',
        #'username': 'nickname',
        'email_address': 'email',
    }
    def __init__( self ):
        """Create the (simplistic) metadata provider"""
        self.mapping = {}
    def register_user( self, open_id, sreg_data ):
        """Add SReg extension data to our mapping information"""
        self.mapping[ open_id ] = sreg_data
        current = model.User.by_user_name( open_id )
        if current:
            # TODO: could update the in-db values...
            if current.password:
                return False
            return True
        else:
            values = self.as_user_values( sreg_data, {} )
            model.DBSession.add(
                model.User(
                    user_name = open_id,
                    **values
                )
            )
            transaction.commit()
            return True
    def as_user_values( self, values, identity ):
        """Given sreg values, convert to User properties"""
        for id_key,sreg_key in self.key_map.items():
            value = values.get( sreg_key )
            if value is not None:
                identity[id_key] = value
        return identity
    def add_metadata( self, environ, identity ):
        """Add our stored metadata to given identity if available"""
        key = identity.get('repoze.who.plugins.openid.userid')
        if key:
            values = self.mapping.get( key )
            if values:
                identity = self.as_user_values( values, identity )
        return identity

Note

The only reason to have the registration part of the metadata provider is that repoze.who doesn’t have a registration plugin-type. Future versions of the plugin might make the registration function separate from the metadata provision by explicitly referencing the registration operation from the OpenID plugin.

Enabling OpenID

We need to alter our who.ini to make use of the various OpenID components. We configure:

  • an identification plugin (which is what actually identifies the user based on their ability to log into the specified server). It intercepts requests based on the configured URLs, as it is application middleware, not controller-based. It stores the identity using the auth_tkt mechanism, as does our regular FriendlyForm identifier
  • our OpenIDMetadata plugin above
  • a challenge decider plugin (which determines whether to invoke the login machinery for a given request)

and then we wire each of those plugins into the main repoze.who machinery.

[plugin:openid]
use = repoze.who.plugins.openid:make_identification_plugin

store = file
store_file_path = %(here)s/sstore
openid_field = openid
came_from_field = came_from
error_field = error
session_name = beaker.session
login_form_url = /login
login_handler_path = /openid_login_handler
logout_handler_path = /logout_handler
logged_in_url = /
logged_out_url = /
rememberer_name = auth_tkt

[plugin:openidmd]
use = customwho.lib.auth:OpenIDMetadata

[plugin:auth_tkt]
use = repoze.who.plugins.auth_tkt:make_plugin
secret = 'this secret is not really very SECRET!'

[plugin:friendlyform]
use = repoze.who.plugins.friendlyform:FriendlyFormPlugin
login_form_url= /login
login_handler_path = /login_handler
logout_handler_path = /logout_handler
rememberer_name = auth_tkt
post_login_url =
post_logout_url =

[plugin:sqlauth]
use = customwho.lib.auth:auth_plugin

# Now the configuration starts wiring together the pieces
[general]
request_classifier = repoze.who.classifiers:default_request_classifier
challenge_decider = repoze.who.plugins.openid.classifiers:openid_challenge_decider

[identifiers]
# We can decide who the user is trying to identify as using either
# a fresh form-post, the session identifier cookie, or a fresh OpenID
# authentication
plugins =
    friendlyform;browser
    openid
    auth_tkt

[authenticators]
# openid and password authentication available
plugins =
    openid
    sqlauth

[challengers]
plugins =
    openid
    friendlyform;browser

[mdproviders]
# We add our custom metadata provider to the set of
# possible metadata providers.
plugins =
    openidmd
    customwho.lib.auth:md_plugin
    customwho.lib.auth:md_group_plugin

Adding the User Interface

../../_images/openid-login.png

We provide an OpenID form on our login page to allow the user to enter their OpenID and log in. We’re using the main “login” template, as it allows us to provide an “alternate” interface where the user of OpenID can login just as readily as any other user. You may prefer to use a separate page for OpenID sign-in, particularly if you wish to provide more instructions or specialized sign-in buttons for certain identity providers:

<form action="${tg.url('/openid_login_handler', came_from = came_from.encode('utf-8'), __logins = login_counter.encode('utf-8'))}" method="POST" class="openid-login">
    <input type="text" id="openid" name="openid" class="text" value="http://"></input>
    <input type="submit" id="submit" value="Login with OpenID" />
        <input type="hidden" value="/" name="returnto"/>
        <input type="hidden" value="claim_openid" name="op"/>
        <input type="hidden" value="1" name="openid_login"/>
        <div class="get-an-openid">
            <a href="http://openid.net/get-an-openid/">Get an OpenID</a>
        </div>
</form>

At this point, we can point our browser at our site’s /login page and see a crude form which allows us to type in an OpenID and authenticate with an OpenID URL.

Note

Most of the major OpenID providers have specified that their users should not be given raw OpenID logins such as seen above. Instead they want to have “Log in with Yahoo” or “Log in with Google” buttons, which under the covers invoke OpenID, but do not require the user to construct or remember OpenID URLs themselves.

Those who have implemented OpenID have fairly consistently reported that user confusion is one of the biggest problems for the system, so if you are going to implement OpenID on your site, plan to spend some time making your interface simple and obvious. You may find that you need to implement the sign-on as a full page with background discussions and examples to avoid user confusion.

Todo

Provide sample code for the “Log in with ...” implementations.

Adding Some Style

OpenID provides a logo suitable for use as a background for text-boxes. We can download this logo to our project’s public/images directory:

wget http://wiki.openid.net/f/openid-16x16.gif

And then reference it from our css stylesheet public/css/style.css to get a reasonable looking and somewhat compact login form:

form.openid-login {
    border: thin solid #f7931e;
    padding: .25em;
}
form.openid-login input[type="text"] {
    padding-left: 16px;
    background: url('/images/openid-16x16.gif') top left no-repeat;
    width: 10em;
}
form.openid-login input[type="submit"] {
    background-color: #f7931e;
    color: white;
}

Todo

Difficulty Medium/Hard: document how to provide group/permission support when using an OpenID Authentication provider.

Todo

Difficulty Hard: document how to store OpenID identifiers in SQLAlchemy (i.e. add records for each new OpenID identity)

References

  • Using who.ini – describes the process to switching to who.ini from quickstart
  • Get an OpenID – describes how to get an OpenID URI via various services, you may already have an OpenID provider. If not myopenid.com can be used to set up a new ID
  • Repoze.who.plugins.openid – documentation for the plugin