Simple Login Registration plugin with only login, registration, password recovery and related features. If you don’t need heavy stuffs like membership, profile etc, then it is ideal for you to keep your site smooth.

Gateman – Simple Login Registration

A lightweight login and registration plugin designed without unnecessary bloat. Just the essential features you need for a smooth user experience.

Functions:
<ul>
<li>Simple LogIn (one click)</li>
<li>Simple LogOut (one click)</li>
<li>Create user automatically</li>
<li>Update user’s profile with the informations that came from Identity Provider</li>
<li>Protect the user’s profile, that the user can’t modificate the informations that came from Identity Provider</li>
<li>Syncronize the LogIn and LogOut actions between the WordPress and the Identity Provider </li>
<li>If the (Apache) agent have a long update period you can choose what to do the plugin: go to login URL or LogIn.</li>
<li>SSL support</li>
<li>Rules: If a regular expression match to the $_SERVER variable’s element put the user to the group.</li>
<li>Plus plugin: Simple Group Manager – Manage the user’s groups and the group’s roles.</li>
<li>Admin page: Users / SSO Autentikáció</li>
</ul>
For more infromation please read this: http://kir-dev.sch.bme.hu/wp-opensso
If you don’t now how it’s work: https://redmine.kirdev.sch.bme.hu:8081/wiki/wordpress/OpenSSO_autentikacio (in Hungarian)

OpenSSO

Authenticate users using  Sun's Open Single Sign On service.

Gateman – Simple Login Registration vs OpenSSO