This will obviously require API version bump but it should not break any applications which use auth.h API.
Patch for osmocom-bb to use auth.h is applied in git. Patch for OpenBSC pending review in the ML.
If there are other open source projects using comp128 directly I'd be to assist with transition, although it's rather trivial - see http://patchwork.ozlabs.org/patch/356029/ for example.
cheers, Max.