Janrain's PHP-OpenID and Google/Yahoo
I'm using Janrain's PHP-OpenID 2.1.3, and I've managed to get it working with all the providers I have tried except for Google and Yahoo. The major difference here seems to be that Google and Yahoo, unlike most other providers, don't use a user-specific URL, but rather have the user discovery framework all on their end - which throws the default Janrain framework for a loop then it tries to begin the auth request.
From what I've seen it looks like it's probably the YADIS discovery that is throwing the error, which should be able to be bypassed since the discovery is on Google or Yahoo's end, but I'm not sure. This is all a big informal learning experience for me, and I haven't had any luck finding documentation that can help me on this one. Any tips would be greatly appreciated.
Edit: the specific problem I am having is that when the begin() function is called for the Google or Yahoo URL, I get a null return. This function is found in Auth/OpenID/Consumer.php for reference.
Answer
Ok, I finally got to fix the library... I explained everything here (you can also download the php-openid library after my changes).
I needed to do what Paul Tarjan suggested but, also, I needed to modify the Auth_OpenID_detectMathLibrary and add the static keyword to a lot of functions. After that It seems to work perfectly although it is not an ideal solution... I think that someone should rewrite the whole library in PHP 5...