Add JOSE VC/VP signature format.

[timothee-haudebourg]

According to W3C's Securing Verifiable Credentials using JOSE and COSE, section 3.1.

[sbihel]

The code looks good. A couple of questions:

• Is https://github.com/w3c/vc-jose-cose-test-suite/ any relevant to add additional tests?
• Do you think there's a way of better integrating with JsonCredentialOrJws or should the user simply manually decode the JWS?

[timothee-haudebourg]

Is https://github.com/w3c/vc-jose-cose-test-suite/ any relevant to add additional tests?

Probably, but I think it will be more useful when we'll have the sd-jwt part of jose-cose implemented

Do you think there's a way of better integrating with JsonCredentialOrJws or should the user simply manually decode the JWS?

I'm not sure yet. There are two JWS signature formats for VC, one defined in VCDM1.1 (JWT-VC) and used by JsonCredentialOrJws, and one in JOSE-COSE for VCDM2.0. If we really need it we could add a similar JsonCredentialOrJws type in the v2 module, but having a single type that can make the distinction between JWT-VC and JOSE-COSE will require some more work.