title: Creating Subscription through Postman throws error
body: <p>Creating WebHook for MicrosoftGraph throws error</p>
  
  <p>What is ClientState represents ?</p>
  
  <pre><code>{
      "changeType": "updated",
      "clientState": "kT]G=3@hClz0rRfOuVr*3UA8V_9UGs4p",
      "expirationDateTime": "2019-09-26T15:46:18.835Z",
      "notificationUrl": "https://webhooksformicrosoftgraph.azurewebsites.net/api/HttpTrigger1",
      "resource": "groups"
  }
  
  {
    "error": {
      "code": "InvalidRequest",
      "message": "Subscription validation request failed. Must respond with 200 OK to this request.",
      "innerError": {
        "request-id": "4f368e23-9a5d-4c72-a2cf-9bbe33f677f4",
        "date": "2019-09-23T06:35:20"
      }
    }
  }
  </code></pre>