Getting logged-in user details in new Web Form

Summary

Getting logged-in user details in new Web Form

Content

Anyone knows how to get logged in user details in new Web Form? I used to do a rest call in basic form and pass the id of the logged-in user by using a decode function as below...

if(form.load) { 

     var loggedinUser = decode(subject.id); 

     eval('user=' + http.get('http://host:port/bpm/api/1.0/identities/user/' + loggedinUser)); 

     UserLastName.value = user.userLastName;

}

How can I do the same in new Web form?

PS: This is a start form, so I cannot pass the user id as a parameter from the process.