GO:0017095:   heparan sulfate 6-O-sulfotransferase activity
Catalysis of the reaction: 3"-phosphoadenosine 5"-phosphosulfate + heparan sulfate = adenosine 3",5"-bisphosphate + heparan sulfate 6-O-sulfate; results in 6-O-sulfation of glucosamine residues in heparan sulfate.