You can clone with
HTTPS or Subversion.
Attempts to log in using GitHub get through to the grant-access stage, then result in an "Invalid Credentials" error message (not sure @ what domain as I haven’t experienced this error myself).
People having these problems:
This has been resolved. There were two problems:
The redirect URI has been updated in the application to https://indieauth.com so Github accepts requests now.
Brilliant, great to hear it!