If you want to use OpenID as an authentication mechanism, but are afraid of the fact that your OpenID provider may die in the future, or you simply might want to use another provider in the future, you can use a delegation model with OpenID.
A reason to change the OpenID provider might be, that your current OpenID provider does not support an authentication mechanism you like to, as for example the YubiKey or something like that.
Let’s say you want to use http://xyz.example.com as your OpenID and you want to use http://clavid.com as your Identity Provider, you have to execute the following steps.
Create a (sub-)domain for example.com called xyz.
This can for example be done by adding another virtual host to your apache configuration. The configuration might look like the following one:
<VirtualHost xx.xx.xx.xx:80>
ServerAdmin webmaster@example.com
ServerName xyz.example.com
DocumentRoot /var/www/xyz/
<Directory /var/www/xyz/>
# Options Indexes MultiViews
AllowOverride None
Order allow,deny
allow from all
</Directory>
ErrorLog /var/log/apache2/error_xyz.log
# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn
CustomLog /var/log/apache2/access_xyz.log combined
</VirtualHost>
Create a index.html file inside your document root
As a next step you have to create a index.html file in your document root (in this case /var/www/xyz) with the following content in order for OpenID services being able to find your current identity provider:
<html>
<head>
<title>Jens' OpenID delegation page</title>
<link rel="openid.server" href="http://www.clavid.com/provider/openid" />
<link rel="openid2.provider" href="http://www.clavid.com/provider/openid" />
<link rel="openid.delegate" href="http://jens.clavid.com" />
<link rel="openid2.local_id" href="http://jens.clavid.com" />
</head>
<body>
<h1>This page is used for OpenID delegation.</h1>
For more information on OpenID either visit
<a href="http://openid.net">http://openid.net<a> or
<a href="http://clavid.com">http://clavid.com</a>
</body>
</html>
Ready
From now on you can use http://xyz.example.com as your OpenID, which will, as currently configured, be redirecting to http://clavid.com where authentication will take place.
References
You can read all about OpenID in the specification, but the part used for this example is available at:
http://openid.net/specs/openid-authentication-1_1.html#delegating_authentication
