In the MDrivenDesigner System prototyper, it is possible to add an expression to simulate login. This will be useful if your logic checks the current user - the prototyping does not identify the current user and requests no login.

Consider this expression in the "Exp to run on start" box:

SysSingleton.oclSingleton.CurrentUser := SysUser.allinstances->select(username='someusername')->first