This is more of a problem with your website than it is your product, but it slowed me down when trying to use your product so I'm considering it an issue of your product :).
I went to sign up, tried to sign in with GitHub and got an error message.
message: "Missing or invalid User Agent string. See http://developer.github.com/v3/#user-agent-required"
That link has a pretty clear solution to the issue, just need to add a UA to the api call.
Thanks Collin, patches have been made for the modules that we use for authentication. We are currently waiting for the project maintainers to accept the pull requests.