Azure Function App (Backend) 401 Error when accessing from Azure App Service Frontend - azure

Question

we have a problem and i dont see anything which i can do for now. I've already followed for example this article but i does not work for now: Azure Function App as Backend
Azure AD Authentication is configured in our Azure Function App and with postman i can connect with a bearer token to the function app.
Function App Authentication is configured with error 401 for apis
I can see in the browser that there is always this error when we open the frontend app. There is no access to the Azure AD secured backend function app from the frontend: Failed to load resource: the server responded with a status of 401 (Unauthorized)
i exposed the api from the app registration of the backend function app and gave them invoke delegated rights to the frontend app registration like in the blog article. CORS is configured too.
App Reg Invoke Config
is there anything i can do? We login to our Frontend App Service with Azure AD credentials and this token should give access to the backend service function app too so there is nothing unprotected in the public internet. But frontend get always this 401 error.

Answer 1

I tried to reproduce the scenario from my end :
When you decode the bearer token ,
Check issuer url and audience received
Also if issuer url has v2 endpoint ,Make sure the accessTokenAcceptedVersion is set to 2 other wise null or 1
Manifest:
{
"id": "4axxxxxxx039",
"acceptMappedClaims": null,
"accessTokenAcceptedVersion": 2,
...
}
Try including function app url https://kafnapprepo.azurewebsites.net
in allowed audiences. Along with the clientId of the app and AppId uri
and make sure the permissions are granted admin consent.