Add support for Google OAuth hd parameter

[craftbyte]

When limiting login to a GApps domain, allow the user to set the hd parameter. This will allow Google to only display accounts on the domain.

Docs: https://developers.google.com/identity/protocols/OpenIDConnect#hd-param

[jehiah]

@craftbyte this sounds useful. Are you interested in contributing support for this?

[craftbyte]

Sadly, I don't know GoLang, but will try :)