Narrow the login process to be supported auth0 providers that have an email address. Save the users' Auth0 parametrs to the users table

[Richard-outreach]

After a user has logged in or signed-up via Auth0, Auth0 calls the service's /callback endpoint with a unique identifier.

Because we do not know if this is a Auth0 "sign-up" or "sign-in", we need to determine if we need to pull user data from Auth0 and persist it in our "Users" DB entry.

If the User already exist in our User table, no-op.
If the User does not exist in our User table, call Auth0 to retrieve the user's information, then persist it in our database.

[sscchan]

Reference: https://auth0.com/docs/api/authentication#get-user-info

[sscchan]

Project Auth0 endpoint: https://seattlevoluntech.auth0.com

[sscchan]

Info on Auth0's flow, especially on getting the token from the callback code.
https://auth0.com/docs/api-auth/tutorials/authorization-code-grant#2-exchange-the-authorization-code-for-an-access-token

[sscchan]

Experimentation indicates LinkedIn Auth0 user profile does not provide email address.