Support empty claims values

[RaphiMC]

Describe the bug
In versions before 0.12.x it was possible to add empty values in the claims of the JWT (for example .claim("test", "") or .claim("test", new ArrayList<>())). In versions after 0.12.0 empty claims are not serialized (compacted) anymore which breaks my use case where the receiving end expects the JWT to have all keys (even ones with empty values) in the claim map.

To Reproduce
Try to create a JWT with some claims that have empty values (See above example)
My exact code: https://github.com/RaphiMC/ViaBedrock/blob/5674c4b0a04f64b5560064ba326d8ac3e6e5403a/src/main/java/net/raphimc/viabedrock/protocol/packets/LoginPackets.java#L341

Expected behavior
I am expecting to be able to add empty values into the claims map (See above example)

[lhazlewood]

@RaphiMC compact JWTs are supposed to be compact/minimal, and having empty claims is counter to providing small payloads.

Is there a reason you can't treat a missing claim as empty?

[RaphiMC]

I need all claims since I don't control the server (Minecraft: Bedrock Edition) thats handling the JWT (I am writing a client which is supposed to be 1:1 the same on the networking level as Minecraft: Bedrock Edition). If the server doesn't receive all claims it will kick me as their parser doesn't implement this case. I used .compact previously as well, is there another method instead of .compact which gets me the JWT with all claims even empty ones?

[lhazlewood]

@RaphiMC this is helpful, thank you. No, there isn't a separate method, we'll have to think about how we can/should support this in a future release.

[lhazlewood]

I'm working on a fix for this, but I noticed something unrelated in the referenced code that looked strange to me:

https://github.com/RaphiMC/ViaBedrock/blob/5674c4b0a04f64b5560064ba326d8ac3e6e5403a/src/main/java/net/raphimc/viabedrock/protocol/packets/LoginPackets.java#L322

x5u is defined in the RFC to be a URL/URI to a resource that contains an X509 Certificate or X509 Certificate chain, not the actual encoded public key value itself.

If you want to include the public key in the header, that's what the jwk header parameter is for, e.g.

EcPublicJwk jwk = Jwks.builder.key(publicKey).build();
Jwts.builder().header().jwk(jwk).and()...

Anyway, just an observation. Do with it what you will 😉 .

[lhazlewood]

This change is in the 0.12.3 release.

[RaphiMC]

Thanks for the quick fix and thanks for looking over the surrounding JWT code and checking it for errors. I just dumped the JWT chain from the original Minecraft: Bedrock Edition client and can confirm that the x5u header field contains the encoded public key and not an URL/URI. I assume Mojang (Devs of the game) just didn't want to mess around with sending multiple requests to external servers from the client and server to verify validity of the JWT chain, so they just broke spec and did their own thing. I can't use the .jwk(jwk) method if it doesn't produce the exact same output as me manually handling the x5u header (Where I assume it produces different output), because the server (Which I am sending the JWT chain to) would have no idea on how to interpet this data and would kick me due to not being able to verify validity of my JWT chain.