The Pentagon had a stop/transfer point on the D.C. metrorail. So did Navy Yard and NNMC(National Naval Medical Center)/Bethesda. Also on the stops were Crystal City and Hoffman which is where Army HR and Finance,Transportation,Logistics offices are. I know its not fair to compare that area since almost everyone there worked for the government in some way whether it was local, or federal, but we would have our fair share of gov. riders too.
The station just had I.D./credential checks as you exit the station if you choose to enter the building; the Pentagon had alot of civilian traffic every day, and I'm sure BAMC and FSH have their fair share too, with the museums, civilian business offices being built such as
Old BAMC II, visitors to the CFI and BAMC and increase in student graduations.
I'm sure if this came to be, BAMC or FSH would have similar checks and if you can't get on Post, you just have to wait for the next car.