Feature/comp 208 google o auth poc

Add support for authentication with OAuth2 providers (using Google as a provider for testing, the final app should use Eduteams)

It's still WIP - user model and simple role-based access has to be created (e.g. allowing someone to sign in, but disallowing them from editing things until manually approved somehow)

compendium_v2/auth/session_management.py

-from flask_login import LoginManager, UserMixin  # type: ignore
+from flask import jsonify
+from datetime import datetime
+from compendium_v2.db import session_scope
+from compendium_v2.db.auth_model import User
+from flask_login import LoginManager  # type: ignore
 
 
-# TODO: implement user model as SQLAlchemy model
-class User(UserMixin):
-    pass
+def create_user(email: str, fullname: str, oidc_sub: str):
+    """
+    Function used to create a new user in the database.
+
+    :param email: The email of the user
+    :param fullname: The full name of the user
+    :param oidc_sub: The OIDC subject identifier (ID) of the user
+    :return: The user object
+    """
+
+    with session_scope() as session:
+        user = User(email=email, fullname=fullname, oidc_sub=oidc_sub)
+        session.add(user)
+        return user
 
 
-def fetch_user(email: str):
+def fetch_user(profile: dict):
+    """
+    Function used to resolve an OIDC profile to a user in the database.
+
+    :param profile: OIDC profile information
+    :return: User object if the user exists, None otherwise.
+    """
+
+    with session_scope() as session:
+        sub_id = profile['sub']
+        user = session.query(User).filter(User.oidc_sub == sub_id).first()
+        if user is None:
+            return None
+        user.last_login = datetime.utcnow()
+        return user
+
+
+def user_loader(user_id: str):
     """
     Function used to retrieve the internal user model for the user attempting login.
 
-    :param profile: The email of the user attempting login.
+    :param user_id: The ID of the user attempting login.
     :return: User object if the user exists, None otherwise.
     """
 
-    # TODO: fetch user from database instead of just creating a user object
-    user = User()
-    user.id = email
-    return user
+    with session_scope() as session:
+        user = session.query(User).filter(User.id == user_id).first()
+        if user is None:
+            return None
+        user.last_login = datetime.utcnow()
+        return user
+
+
+def unauth_handler():
+    return jsonify(success=False,
+                   data={'login_required': True},
+                   message='Authorize to access this page.'), 401
 
 
 def setup_login_manager(login_manager: LoginManager):
 
-    login_manager.user_loader(fetch_user)
+    login_manager.user_loader(user_loader)
+    login_manager.unauthorized_handler(unauth_handler)