Support JWS JSON Serialization

[lukasjhan]

In sd-jwt draft 09 section 9, JSON Serialization method is added. Let's support this feature in our library

[lukasjhan]

There are two kinds of serialization, flatten and general.

I was thinking about adding the converting function between:

• SD-JWT <=> JWS flatten serialization
• SD-JWT <=> JWS general serialization

What do you think about it? @cre8

[cre8]

That does not make so much sense:
A generalised Json serialisation can have multiple issuer signatures (required for jades signature). So we can not transfer from this to compact when there are more than one. With flattened it should be possible.

I started the implementation that you pass the issuance function a value what kind of type do you want and the return value is based on this.

Then we need to update the decode function and verify so the three options can be consumed. The default one should be compact to not break any existing implementations

[lukasjhan]

Yeah, you're right. A generalised Json serialisation can have multiple signatures. So there is a possibility that it cannot be converted to a compact one.

I think it's better to approach it the way you said. :)

[cre8]

I have implemented it for the issuance, but decoding and tests are missing. Maybe I am able to create a pr until Friday

[lukasjhan]

To prevent too many changes to the internal implementation, I'm considering creating a new class for JWS JSON-related functions.

[cre8]

I don't think that is possible, see my current PR. The jwt object needs to hold multiple signatures, so we need to touch some of the core classes