title: Azure Web App EasyAuth callback throws error
body: <p>I have an ASP.NET MVC app, running as Azure Web App.</p>
  
  <p>I use pre-authentication/EasyAuth, and for 5 deployment slots it works fine. Each of them has their own Azure AD App Registration.</p>
  
  <p>But the production site (not a deployment slot, root of the app) throws an error when after logging in, at the <code>/.auth/login/aad/callback</code> path:
  <a href="https://i.stack.imgur.com/7acUP.png" rel="noreferrer"><img src="https://i.stack.imgur.com/7acUP.png" alt="pre-auth callback fail"></a></p>
  
  <p>I have compared Azure AD App manifest with one that works, and the only difference is the names, description and URLs - as expected.</p>
  
  <p>Using Kudu to view an error, it seems to come from the <code>EasyAuthModule</code>:
  <a href="https://i.stack.imgur.com/yOzfx.png" rel="noreferrer"><img src="https://i.stack.imgur.com/yOzfx.png" alt="enter image description here"></a></p>