[Litmus Portal] Authentication Module Refactor and OAuth Implementation

The Authentication server of the litmus portal (which resides in the litmus-portal folder of the main litmus repository) is written in golang, uses certain outdated dependencies (such as mgo), and currently does not support third-party OAuth authentication modules such as:

• Google Authentication
• GitHub Authentication
• Local Authentication

The current implementation of the authentication server also consumes more resources than the litmus portal’s GraphQL server.

This proposal shall focus on re-writing the Authentication Module of the litmus-portal so that it achieves the following:

• The Authentication Module is Independent (Can be moved to a separate repository)
• The Module is light-weight and makes use of actively maintained dependencies (if any)
• The Authentication Server is robust and flexible to any future addition of features
• The Authentication Server supports OAuth authentication such as Google Auth and GitHub Auth