I have an ASP.NET MVC app, running as Azure Web App.

I use pre-authentication/EasyAuth, and for 5 deployment slots it works fine. Each of them has their own Azure AD App Registration.

But the production site (not a deployment slot, root of the app) throws an error when after logging in, at the `/.auth/login/aad/callback` path:
[![pre-auth callback fail](https://i.stack.imgur.com/7acUP.png)](https://i.stack.imgur.com/7acUP.png)

I have compared Azure AD App manifest with one that works, and the only difference is the names, description and URLs - as expected.

Using Kudu to view an error, it seems to come from the `EasyAuthModule`:
[![enter image description here](https://i.stack.imgur.com/yOzfx.png)](https://i.stack.imgur.com/yOzfx.png)