The CFR reads in its entirety:
§ 102–74.440 What is the policy concerning weapons on Federal property?
Federal law prohibits the possession of firearms or other dangerous weapons in Federal facilities and Federal court facilities by all persons not specifically authorized by 18 U.S.C. 930. Violators will be subject to fine and/or imprisonment for periods up to five (5) years.
While the wording suggests that "in
" means, within a structure, I can't say how the courts may have already ruled on this. Apparently, neither can you.
Besides the obvious question, "Do you want to be a test case?" it's not yet even time to file for a civil rights violation (which will be costly).
"Why not?", you might very well ask.
Currently, we have several cases before the Circuit Courts of Appeal that may very well answer the question of whether or not we have the right to carry functional firearms, in case of confrontation, in the public space. A positive answer here, will have reaching effects on government parking lots.
More to the point, the Case Bonidy v. U.S.P.S.
directly attacks such a provision as you have outlined (dispositive motions are due this coming Tuesday, the 28th).
The bottom line is that no one can honestly answer your question, at this time.