title: Flask-Login How to check if a user has a certain attribute value
body: <p>i am currently using flask-login for the Authentication of my website.
  My Model is a simple User (with id, mail etc) which has an admin(boolean) attribute.
  I dont need more than 2 Roles.</p>
  <p>Is there any way to check after a route was called, if the current user has the value &quot;True&quot; at the admin attribute?</p>
  <p>I tried solving this issue with trying out custom decorator, as well as accessing session['admin'] , but it did not work.</p>