When I say "minting a token", I mean taking some data (e.g. your user name), adding some metadata (audience, expiry), and performing some operation on it (signing, encryption, authenticating) such that a different party will accept it as-is. (This is like "minting" because if you have a plausible-looking coin people would just accept it without having to go ask the issuer if it's a real coin via serial number or whatever.)
When you generate a random key, you have to go ask a trusted third party what the data associated with that key is (and, therefore, if it's still valid).
Minting tokens is bad because it's drastically more complicated, has tons of failure modes, and most of the time you end up doing tons more database transactions anyway that are way more complicated than set membership (i.e. is this still a valid token?).
In this context then, what are your thoughts on minting tokens using Macaroons [0]? I ask because they seem to be of much lower complexity than JWTs since they just hash the data so no encryption algorithm negotiation or anything of the like, however they still meet your definition of minting a token.
Obviously it would depend on a case-by-case basis to prefer macaroons over say a random token or vice versa, but in general is chaining HMACS still considered "drastically more complicated"?
My uninformed opinion is that verifying a hash shouldn't be that bad but my security expertise is pretty much non-existent so it would be great to be schooled on this :)
If you're going to mint a token, macaroons are a great spec. But when designing a critical security system, the default should be the simplest possible thing, and DB lookup is still much simpler than macaroons. So, you have to have a big problem that macaroons solve first. In my experience, the cure is worse than the disease here.
I did extensive research on various token types including Macaroons. While Macaroons look simple on the surface there are numerous edge cases that the verifier should take care of (Macaroons form a DAG because you can have multiple ones referencing each other). Plus there is symmetric decryption going on in case of third-party caveats. The caveat system can be very powerful (as caveats are just byte arrays you can use any system to encode claims). But there is no standard to encode them and that causes tight coupling between systems using Macaroons. I can go into more detail if that's interesting for someone.
I've read about Macaroons and the lack of a standard to encode caveats (mainly from the google group about macaroons) but I'm interested in your take, so more details would be great!
If you compare it to JWT in JWT claims are basically a string name (like "exp") and a JSON value. It's pretty simple. You need to check of the value for exp is a number and is greater than current millis. In Macaroons the entire caveat (a.k.a. claim) is just a byte array. The majority of libraries use predicates "X op Y" encoded in UTF-8 (e.g. time < xyz, account = 12345). That looks good, in JWT you don't have relation encoded, you just need to know that for exp it's "less than" and for aud it's equals.
Unfortunately that's where the simplicity of Macaroons end because even the official docs on libmacaroons have some weird choices, like encoding date in a ISO-like format (without timezone specifier at all). Also using UTF-8 is not that efficient if one could encode date as a number. Of course Macaroons are flexible and because the caveats are byte arrays you can use CBOR or whatever to conserve space. But then you lose compatibility. And you need compatibility if you want to utilize third party Macaroons (if a third party mints you a Macaroon with unknown caveat that makes the entire thing invalid). Third party Macaroons are the most powerful feature of the entire system but they introduce a lot of complexity: Macaroon references (look out for loops!), symmetric decryption and out of band communication needed to collect everything needed to authorize. That's why existing libraries allow only limited subset (e.g. no third party caveats referencing other third party Macaroons), and if you're writing a library (as I did) there is a lot of reverse engineering (e.g. libsodium is used in most libraries for symmetric encryption).
There are also some small things like de facto implementations using slightly different operations than the paper and a custom binary format. JWT just uses JSON and base64. (For the record I'm not a big fan of JWT).
What I like in Macaroons is the ability to further confine permissions. Sadly PAST doesn't seem to have something like this instead opting for a "safe JWT" way.
One of the issues that I saw being discussed on the forums was precisely the lack of a standard format for caveats and even some suggestions to create one.
I think it's a very cool project but for some reason I don't think it has caught on. Do you think if someone came up with a suitable standard built it would see broader use? or what is your take on the lack of interest (IMHO) for this awesome idea?
Edit: Any way I could contact you to discuss this a bit more, if you are open to it? :)
Macaroons have many moving pieces, caveats being just one of them. Standardization would have to approach it from all edges. For example the binary format while simple is also "de facto" standard resembling protobuf but not exactly. Maybe CBOR would be a good idea (or a subset of it)?
As for caveats there are two forces at place: some want simple format ("X op Y") but there is another way that I've explored in a PoC - use simple stack-based script system (similar to Bitcoin Script [0]), then you can encode some really interesting properties inside your tokens (like requiring hashes of different properties, or signatures) so it would be kind of a meta-authorization scheme where you can delay the decision (e.g. require EC signatures for some sensitive operations). Of course this brings additional complexity but on the other hand using caveats in "X op Y" form doesn't bring any benefits over JWT claims.
The ultimate reason why I abandoned Macaroons (after working for some prototypes and creating a JS library for them) is just the amount of complexity needed to work with them. And remember - code working with Macaroons is being executed before the request is authorized (that's what they are for) so this code need to be carefully audited and any bug can have severe consequences.
Compare that with JWT, you can write a verifier in simple code (JSON and base64 are built-in in any language) and simple is easier to audit. In Macaroons you first need to decode base64, parse custom binary format, check consistency (no cycles in third-party caveats), decrypt third-party keys. Moreover there can be multiple Macaroons for given ID, you need to check if at least one satisfies the request. Better - check all of them and then see if at least one works (to protect against side-channel attacks). So there is some inherent complexity in the entire stack. Removing it would require some substantial work. IMHO that's why they are not widely used. Oh, did I mention the existing libraries have some rather significant issues [1]?
So to answer your question: I would gladly see some standarization effort, but it needs to be really thorough to have good effect. Unfortunately Macaroons are already plagued by old cruft (e.g. third-party caveats ID are called "cid" and first party caveats are also called "cid" but they are completely different) that no-one wants to touch not to break existing code.
If you don't mind we can keep the discussion here, it's good for others to see (I got into Macaroons because of one of these threads) and it's google-able :)
When you generate a random key, you have to go ask a trusted third party what the data associated with that key is (and, therefore, if it's still valid).
Minting tokens is bad because it's drastically more complicated, has tons of failure modes, and most of the time you end up doing tons more database transactions anyway that are way more complicated than set membership (i.e. is this still a valid token?).