I didn't want to hijack the CAS thread, but I came here looking for similar information. With the XenForo add-on system, is it possible to integrate an SSO solution? 1) Using XenForo as the master user base wouldn't be that difficult as long as we had a way we could securely test in an external PHP script/app if a user is logged in, and then get that user info for the external system to use for SSO. Question: Can these tests be done from external scripts on the same top level domain? 2) Using an external app as the master user base would be a lot more complicated I'm sure as there would need to be ways to hook code into the login/register/update screens, or a way to entirely substitute those pages with the external app. Who knows what the external app is going to be so how can you plan for that huh? It would be helpful even if there was basic support for auto-logging in/adding a user from an add-on could be done. Then maybe a redirect option for basic the basic account info like username, email, & password. Question: I understand #2 is a fluffy question, but is this being considered with this software? SSO support would definitely open up a new range of potential clients for this software.