Fedora accounts system provides OpenID authentication. If you are using python-fedora to do authentication in your webapp, you already know what I am talking about. I wanted to do the same, but from a webservice written in golang. I found a few working openid solutions in golang but none of them provides the sreg and other extensions which FAS supports.
I pushed patched openid.go in my github which by default supports all the extensions for FAS. We have an example which shows how to access the Verify function and the output. Now you can have FAS authentication if your app too :)
id, err := openid.Verify( fullUrl, discoveryCache, nonceStore)