That abstraction is also a strength. I think one of the reasons Macaroons really resonate with security engineers is that the underlying cryptography is simple and user-proof, and the resulting formats and protocols are super flexible†, which is not a combination you typically get with cryptosystems. It's also one of the truly great security papers; having worked with a team for a year scaling them out, I get something new every time I read it. My only quibble is the internal naming ("CID", "VID").

We're doing a big-ass blog post as we speak about how our Macaroon tokens work, and it covers how we worked around the issuer/verifier constraint (spoiler: a litefs-backed replicated isolated internal API) and we did basic stuff like encoding (spoiler: we defined a rigid struct schema, and just MsgPack'd it).

One of the things I think I have to say about Macaroons is that there's a sliding scale of how much you use it; I think there are some simple ideas in them that would be pretty neat in any application's authentication cookie scheme.

† Also one of a couple reasons, I think, that "standard Macaroons" and their associated libraries never went anywhere.