SharePoint 2013 custom workflow (Sequential) visual studio not assigning task

Question

I am creating a simple sequential workflow using VS 2015 in SP2013 on premise. Trying to assign a task to the user in a 'Domain\username' format. The problem is that it is creating a task but not assigning it to the specified user.

createTask1_TaskProperties1.AssignedTo = "Domain"+"\"+"username";

so when an item is added workflow is in progress and when you click on it you can see the task but 'Assigned to' column is empty.

I have tested assigning it to many users (Production users, test users). its only working with one live account of my colleague. that account was site collection admin so I added other test accounts and live accounts as site collection admin. it dint work.

I created a SharePoint group and assigned by retreiving from that group but still no luck. I used our own AD framework to retrieve the users and assign a task, but still no luck. I checked the logs and I compared the account for which it is working with the other which is not working and there is not much in the logs too: I will post the logs here Please see the logs below for working user and non working user: Please check and help me out as I am banging my head over this for two days.

Answer 1

For completeness:

If claims are enabled, you need to provide the full claim, not only the "simple" login. Encoding the claim can be done via ConvertIdentifierToClaim. Whether claims are needed or not can be tested via UseClaimsAuthentication:

var userAccount = "domain\\user"
SPUser user;
if (web.Site.WebApplication.UseClaimsAuthentication)
{
  var claim = SPClaimProviderManager.Local.ConvertIdentifierToClaim(userAccount, SPIdentifierTypes.WindowsSamAccountName);
  user = web.EnsureUser(claim.ToEncodedString());
} else {
  user = web.EnsureUser(userAccount);
}

Now, the user is available in the web (so you're sure it can be assigned tasks). Use user.LoginName as assignee.