Some applications have been tied to the SharePoint Intranet site allowing folks to use their Office 365, RCDA login to provide access to the application.

This is made possible by the fact that the sharepoint site displays the identity of the currenly logged in user.

Using some javascript and an HTML form, I can send the user's name and a special code to the application which exists outside the SharePoint environment and determine whether or not the user should be granted access to the application.