Rework user types: create AuthenticatedUser and AnonymousUser class

Both are subclasses of an abstract User class which contains almost everything
interesting.

express/request/index.ts

@@ -1,13 +1,13 @@
 import { AuthService } from "../auth";
 import { getCurrentUser } from "../context";
 import { PostgresAuthStore } from "../database";
-import type { MaybeUser } from "../user";
+import type { User } from "../user";
 import { html, redirect, render } from "./util";
 
 const util = { html, redirect, render };
 
 const session = {
-    getUser: (): MaybeUser => {
+    getUser: (): User => {
         return getCurrentUser();
     },
 };