verify the users Firebase JWT and store the session
sign_in_social(firebase_token, hashed_cookie)NULL if sign in fails. If sign in is successful, a list containing the following:
email_verified
is_admin
user_uid
hashed_cookie
session_uid
the Firebase JWT. This JWT is created client side
(in JavaScript) via firebase.auth().
the hashed polished cookie. Used for tracking the user
session. This cookie is inserted into the "polished.sessions" table if the
JWT is valid.