Document authentication approach

[qgolsteyn]

Description

We need to add authentication for this project. Look at various providers for third party auth, document what is needed to get it working on a React native project, and show a simple implementation of it working.

Specifically, we want to know:

• How to trigger it, what payload do we need to provide and what API we should contact
• What data we get back when the user successfully logged in and when authentication failed.
• Map the error messages we might need to handle (ie. no network connection, failed authentication)
• Figure out how we can get simple user info (profile picture, user name, email address).

Dependencies

Acceptance criteria

• Add relevant documentation to this issue as described above
• Document decision in the SPECS document
• Stretch goal: implement a simple auth workflow in React Native, or point to an existing implementation

[no-or]

We can use Firebase Auth:
https://firebase.google.com/docs/auth

There are good documentation and tutorials online so integrating this shouldn't be a problem