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/__init__.py

+from flask import Flask
+from authlib.integrations.flask_client import OAuth, FlaskOAuth2App  # type: ignore
+
+oauth = None  # type: OAuth
+
+
+def setup_oauth(app: Flask, oidc_config: dict):
+    global oauth
+
+    if oauth is not None:
+        return
+
+    oauth = OAuth(app)
+
+    if oidc_config is None:
+        return
+
+    oauth.register(
+        name='provider',
+        client_id=oidc_config['client_id'],
+        client_secret=oidc_config['client_secret'],
+        server_metadata_url=oidc_config['server_metadata_url'],
+        client_kwargs={
+            'scope': ' '.join([
+                'email',
+                'profile'
+            ])},
+    )
+
+
+def get_client() -> FlaskOAuth2App:
+    return oauth.create_client('provider')