First, In the WorkflowGen site, make sure that you are using IIS authentication mode in the the Admin section Configuration Panel → General → Authentication → Mode
Second, in IIS, click on the WorkflowGen site then “Authentication” feature under the IIS section:
Disable all authentications and only enable Windows Authentication.
This setup will not work with Windows Integrated since the system won’t be able to identify the user.
A good solution to make it work with Windows authentication is to give the users remote access to their work computer. They would be able to login in their work computer remotely and authenticate successfully with Windows authentication.