title: I get an error code 401 when create a call use graph explorer
body: <p>I try to create a call using graph explorer, but i get an error code 401 and 
  a message as "Looks like you may not have the permissions for this call. Please modify your permissions. "</p>
  
  <p>I already  set permissions through Azure active directory. </p>
  
  <pre><code>Calls.Initiate.All
  Calls.InitiateGroupCall.All
  Calls.JoinGroupCall.All
  Calls.JoinGroupCallAsGuest.All
  </code></pre>
  
  <p>request as follows:</p>
  
  <pre><code>POST https://graph.microsoft.com/beta/app/calls
  Content-Type: application/json
  
  {
    "callbackUri": "https://bot.contoso.com/api/calls",
    "mediaConfig": {
      "@odata.type": "#microsoft.graph.appHostedMediaConfig",
      "blob": "&lt;media config blob&gt;"
    },
    "requestedModalities": [ "audio" ],
    "source": {
      "identity": {
        "application": {
          "id": "MyRealApplicationCode",
          "tenantId": MyRealTenantId,
          "displayName": "IT Bot"
        }
      },
      "languageId": "languageId-value",
      "region": "region-value"
    },
    "subject": "Test Call",
    "targets": [
      {
        "identity": {
          "user": {
            "id": "MyRealUserId",
            "tenantId": MyRealTenantId,
            "displayName": "Heidi Steen"
          }
        }
      }
    ],
    "tenantId": "tenantId-value"
  }
  </code></pre>
  
  <p>response as follows:</p>
  
  <pre><code>{
      "error": {
          "code": "UnknownError",
          "message": "{\"errorCode\":\"9000\",\"message\":\"Unsupported AAD Identity.\",\"instanceAnnotations\":[]}",
          "innerError": {
              "request-id": "b0232477-048b-486b-9d43-77aacfb3fa2f",
              "date": "2019-07-16T06:44:00"
          }
      }
  }
  </code></pre>