Add Shibboleth login button plugin

This plugin adds a button to allow users to login to Chamilo through Shibboleth authentication.

You have to configure your Shibboleth connexion before using this plugin.

To activate and configure Shibboleth, for your Chamilo platform, go to Administration > Configuration settings > Shibboleth

This plugin has been done to be added in the login_top region, but you can put it where you want.