Trigger workflow for an item in the list by using CSOM. (env: SP 2013 on-prem, provider hosted app) and App Only will not work

This post is a contribution from Manish Joshi, an engineer with the SharePoint Developer Support team

There seems to be a check in SharePoint when starting a workflow using CSOM if SharePoint 2013 workflow is started using the App-Only context – if yes, throw Access Denied exception and log this exception.

So there is no other way than to start a SharePoint 2013 workflow in CSOM except using the App+User context

Following code illustrates using an app only access token to create a ClientContext and start the SharePoint 2013 workflow in CSOM.

1. Get the Client Context using the App only Access Token

    // get app only access token by passing the windows identity as null
   string appOnlyAccessToken = TokenHelper.GetS2SAccessTokenWithWindowsIdentity(hostWeb, null);
   return TokenHelper.GetClientContextWithAccessToken(hostWeb.ToString(), appOnlyAccessToken); 
   

    

2. Invoke the workflow using the Client Context retrieved

    // start the workflow using the CSOM APIs and the client context retrieved previously
   var workflowManager = new WorkflowServicesManager(clientContext, clientContext.Web);
   InteropService workflowInteropService = workflowManager.GetWorkflowInteropService();
   
   // call the StartWorkflow method   - https://msdn.microsoft.com/en-us/library/office/microsoft.sharepoint.client.workflowservices.interopservice.startworkflow.aspx
   workflowInteropService.StartWorkflow(workflowAssociation.Name, corId, list.Id, itemGuid, new Dictionary<string, object>());
   clientContext.ExecuteQuery();
   

    

The above code will throw AccessDenied exception.

To get this to work the code needs to be changed as below.

1. Get the Client Context for App + User context access token

    // pass a valid windows identity to get app + user context
   string appUserAccessToken = TokenHelper.GetS2SAccessTokenWithWindowsIdentity(hostWeb, windowsIdentity);
   return TokenHelper.GetClientContextWithAccessToken(hostWeb.ToString(), appUserAccessToken);
   

    

2. Invoke the workflow using the Client Context retrieved

    // start the workflow using the CSOM APIs and the client context retrieved previously
   var workflowManager = new WorkflowServicesManager(clientContext, clientContext.Web);
   InteropService workflowInteropService = workflowManager.GetWorkflowInteropService();
   
   // call the StartWorkflow method   - https://msdn.microsoft.com/en-us/library/office/microsoft.sharepoint.client.workflowservices.interopservice.startworkflow.aspx 
   workflowInteropService.StartWorkflow(workflowAssociation.Name, corId, list.Id, itemGuid, new Dictionary<string, object>());
   clientContext.ExecuteQuery();