Overhaul domain authentication to allow for more methods of authentication

[Armored-Dragon]

This is a parent issue to corral all client to server authentication issues to keep track of all of the changes under consideration.
The idea is to extend the authentication flow to allow for more easy addition of additional authentication methods. It would also be a good opportunity to clean up a lot of the existing authentication code to something more streamlined. The target of this is specifically domains, but the ideas here can be applied to the directory service in the future.

• Replace Wordpress for domain security with generic OAuth2 #1157
• Finish DTLS for secure client to domain communication #1191 - Important for security