Create authentication service

[briri]

Use the authentication-zero gem to create an authentication service. Since we do not need all of the views and overhead that Devise pulls into an app, we can build a lighter-weight and more transparent auth service.

Use cases for auth are:

• Standard user account creation (via Shib OAuth, username+password)
• Login (via Shib OAuth, username+password)
• Password resets
• Account deletion
• Code -> Token exchange (OAuth code flow) for UI as well as some external partner integrations
• Creds -> Token exchange (OAuth client credentials flow) for external system integrations

[briri]

closing this one since we are not going to use rails as our backend. New corresponding tickets will be opened in each of the 3 new repositories