Hi,
this may help. - Im thinking this is what your asking for.
within the project - in my case its a workflow rather than a webform I add in a 'Dialog Workflow'
double click this.
then go to the second tab - Interaction Setup. then first '...' on the tab. in to Dialog Model.
this opens a new embedded model.
from in here add in the Windows Domain Login Component. - put it in the flow and right click it click edit component.
in domains add in your domain/s
for now put the log in success and failure to the enddialogworkflowcomponent
then add in a ' form Builder' in line after the login success.
in the Variables bottom left of the screen there is [Global] > LastUser. tick this and drag it on to the white space and when it asks select LabelBuilder [String]
to test it and run in production you will need to set the workflow type on the Publishing tab to 'form start'
This will then when you sussesfully login show you the login name of the User currently logged in.
Passing this authentication to other forms is simple because the standard login box uses the same cookie therefore I login to one of my workflows and then flick to the other it keeps me logged in.
see the attached ( remove the .zip extension and import it)