The SSO Checker provides a method for validating the results returned by the SSO subsystem. It will typically notify your in more detail about what is being returned by different plugins, including the exact username that a particular plugin is detecting. This diagnostic requires the JAuthTools libraries and plugins to be installed before it will operate correctly. Using this diagnostic without these plugins installed will result in errors.

The first screen displays some information about the extension and provides a validate user button. As SSO requests within Joomla! do not accept any user level parameters, this is the only input required. Upon clicking this button the page will reload and display the results of the operation:

 From this we can see that the eDir LDAP plugin has returned the username 'MOFFATS' whilst the HTTP plugin hasn't managed to detect a user. As the only return value of a SSO plugin is in fact a username this is all of the information. If this is detecting your user properly then there is potentially an issue with your user source plugins.