Symptoms

"The request failed with HTTP status 401: Unauthorized" getting logged in K2 logs almost every time a SmartObject runs in InfoPath
 

Diagnoses

"The request failed with HTTP status 401: Unauthorized" getting logged in K2 logs almost every time a SmartObject runs in InfoPath.
I'm seeing a lot of "The request failed with HTTP status 401: Unauthorized" events getting logged in the K2 Host Server logs, looks like every SharePoint SmartObject call generates it. For example, the following logs happen every time I open the Server Build InfoPath form... And I believe there are two drop downs that use SmartObjects to display SharePoint list items.

"16783722","2015-10-28 11:08:39","Error","SmartObjects","10702","Error","SourceCode.SmartObjects.ServiceBroker rExecuteSmartObject]","10702 An error occurred in the eServiceInstance Name] Service Instance. The request failed with HTTP status 401: Unauthorized.","anonymous","0.0.0.0","HOSPAPP01:C:Program Files (x86)K2 blackpearlHost ServerBin","16783722","4891e8bda47b44b983ee288f1aaa4bc2",""

I will find similar logs for every InfoPath form using SharePoint SmartObjects. The only SmartObjects that don't seem to log anything are the ones to a SQL database.

 

Resolution

This is expected behavior.
PTA (Pass-Through Authentication) will only kick in when a 401 error occurs.
The server looks out for this error and the second it happens it will 'fall back' to the K2Service Account.

This is for instance what you will see in the hostserver first.
10702 An error occurred in the SharePointGroupsService Service Instance. The request failed with HTTP status 401: Unauthorized.

There after you will see the following.
10700 Service Broker will retry the SharePointGroupsService Service Instance as the K2 Service Account, in case failure was due to delegation issues.

After successful execution with the service account you will see the following.
10046 SmartObject execution event raised successfully.