Today was trying to authenticate my Azure Function app with a User Assigned Managed Identity using the newer Azure.Idenity NuGet package.
Quickly I ran into the following error:
Exception while executing function: MyFunction ManagedIdentityCredential authentication failed: No MSI found for specified ClientId/ResourceId.Status: 400 (Bad Request)
Solution
Add AZURE_CLIENT_ID to the Application settings with the Client ID of the User Assigned Managed Identity as the value:

In order to get the CallBackURL of an HTTP triggered Logic App in a Bicep script use:
listCallbackURL('${myLogicApp.id}/triggers/manual', '2017-07-01').value
(The API version depends on the version of your Logic App.)
For a full Bicep example see: