Create a new auth implementation that validates a JWT token and attaches a user to the global context

[chouinar]

Summary

TODO - some of the technical details.

We want a new auth approach that we can use as an alternative to our current:
@opportunity_blueprint.auth_required(api_key_auth)

Instead we should have a jwt auth that we can attach to our routes. This will do a few things:

• Fetch a token from a header param
• Validate that the token is one we generated in our API (see Setup logic to generate a JWT in our API #2808 )
• Fetch a user from the DB with the given user ID
  • Attach this user object to the global context to be fetched elsewhere

Open questions:

• How does this work with the DB session management, we should be able to get a DB session in other methods, but will the user itself be funky because of a detached session issue?

Acceptance criteria

• Auth implementation created
• Thorough unit tests written to verify edge case scenarios