Bot service with user assigned identity

Question

I'm currently trying to set up a new teams bot with user assigned identity and while I can retrive messages I can't reply back.

I have created a new Azure Bot service in azure, set it to UserAssignedMSI and I have managed to add it to teams. If I send something to the bot I can also see that the methods like OnTurnAsync and OnMessageActivityAsync are triggered so everything looks good so far.

But the moment I try to send something back, like for example:

   protected override async Task OnMessageActivityAsync(ITurnContext<IMessageActivity> turnContext, CancellationToken cancellationToken)  
       {  
           await turnContext.SendActivityAsync(MessageFactory.Text("hello"), cancellationToken);  
           await base.OnMessageActivityAsync(turnContext, cancellationToken);  
       }  

It crash with the following:

   System.ArgumentNullException: Value cannot be null. (Parameter 'clientSecret')  
      at Microsoft.IdentityModel.Clients.ActiveDirectory.ClientCredential..ctor(String clientId, String clientSecret)  
      at Microsoft.Bot.Connector.Authentication.MicrosoftAppCredentials.<BuildAuthenticator>b__16_0()  
      at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)  
      at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)  
      at System.Lazy`1.CreateValue()  
      at System.Lazy`1.get_Value()  
      at Microsoft.Bot.Connector.Authentication.AppCredentials.<BuildIAuthenticator>b__36_0()  
      at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)  
      at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)  
      at System.Lazy`1.CreateValue()  
      at System.Lazy`1.get_Value()  
      at Microsoft.Bot.Connector.Authentication.AppCredentials.GetTokenAsync(Boolean forceRefresh)  
      at Microsoft.Bot.Connector.Authentication.AppCredentials.ProcessHttpRequestAsync(HttpRequestMessage request, CancellationToken cancellationToken)  
      at Microsoft.Bot.Connector.Conversations.ReplyToActivityWithHttpMessagesAsync(String conversationId, String activityId, Activity activity, Dictionary`2 customHeaders, CancellationToken cancellationToken)  
      at Microsoft.Bot.Connector.ConversationsExtensions.ReplyToActivityAsync(IConversations operations, String conversationId, String activityId, Activity activity, CancellationToken cancellationToken)  
      at Microsoft.Bot.Builder.BotFrameworkAdapter.SendActivitiesAsync(ITurnContext turnContext, Activity[] activities, CancellationToken cancellationToken)  
      at Microsoft.Bot.Builder.TurnContext.<>c__DisplayClass31_0.<<SendActivitiesAsync>g__SendActivitiesThroughAdapter|1>d.MoveNext()  
   \--- End of stack trace from previous location ---  
      at Microsoft.Bot.Builder.TurnContext.SendActivityAsync(IActivity activity, CancellationToken cancellationToken)  
      at iPMC.Autotest.DevOps.Bots.Bots.AutotestBot.OnMessageActivityAsync(ITurnContext`1 turnContext, CancellationToken cancellationToken)  

And I'm note sure why. According to the documentation this should be enough in my appsettings.json when using user assigned identity (AVALUE is of course my real values):

   "MicrosoftAppType": "UserAssignedMSI",  
     "MicrosoftAppId": "AVALUE",  
     "MicrosoftAppTenantId": "AVALUE",  
     "MicrosoftAppPassword": "",  
     "ConnectionName": "AVALUE"  

It's seems like most examples use password (single/multi tenant) as well so I can't really find anyone else that have used this.

I have also tried to both do it locally and deployed but I get the same exception on both places so I'm running out of ideas what I should test next.

Anyone else that have used UserAssignedMSI with teams bots and got it to work?