Refactor auth code to be cleaner and more extensible

We move all the auth handling, serialization and deserialization into a new AuthContext interface, and then standardize a registration model for handling of specific auth context types (user, robot, token, etc).

app.py

@@ -6,12 +6,11 @@ import os
 from functools import partial
 
 from Crypto.PublicKey import RSA
-from flask import Flask, request, Request, _request_ctx_stack
-from flask_login import LoginManager, UserMixin
+from flask import Flask, request, Request
+from flask_login import LoginManager
 from flask_mail import Mail
 from flask_principal import Principal
 from jwkest.jwk import RSAKey
-from werkzeug.routing import BaseConverter
 
 import features
 from _init import CONF_DIR