make path_nested path relative in the presentation submission example

[nemqe]

resolves #57

[Sakurann]

I think the current examples are correct because the whole point is to say whether it is [0] or [1] in the VP Token..

[nemqe]

I think that the path_nested needs to be scoped to the upper level of path_nested, i.e. if we have a presentation at index [0] of a vp_token, the credential we are pointing to needs to be contained in that presentation, and it cannot escape that 'sandbox'.

Maybe I am reading the spec wrong: https://identity.foundation/presentation-exchange/spec/v2.0.0/#presentation-submission, but I mostly opened this PR to get clarity on this.

[Sakurann]

@sudeshrshetty to review

[sudeshrshetty]

In OID4VP, presentation_submission and VerifiablePresentation(s) are part of different objects unlike those given in Presentation Exchange Examples.

In case of multiple presentations in vp_token, paths like [0], [1] are necessary.
But path_nested property always provides a relative path within a given nested value, so changes in this PR makes sense to me.

[jogu]

This has unfortunately now conflicted with https://github.com/openid/OpenID4VP/pull/198/files - are you able to resolve the conflict please @nemqe ?

[nemqe]

@jogu conflict resolved

[jogu]

Thank you!

Is it definitely right how it is now:

{
  "id": "Presentation example 2",
  "definition_id": "Example with multiple VPs",
  "descriptor_map": [
    {
      "id": "ID Card with constraints",
      "format": "ldp_vp",
       "path": "$[0]",
       "path_nested": {
         "format": "ldp_vc",
         "path": "$.verifiableCredential[0]"
       }
     },
     {
      "id": "Example credential disclosing only address",
      "format": "vc+sd-jwt",
      "path": "$[1]"
    }
  ]
}

It's confusing me as I thought $ basically referred to the root of the response, can that be accessed as both an array ($[1]) and a object ($.verifiableCredential) ?

[nemqe]

My understanding is that when path_nested you are 'sandboxed' inside of the object specified by path, and that your path is always relative to the 'nesting'.

In this particular example it would mean that path_nested.path=$ is not referring to the root, but to the path=$[0].

I think using $[0] would be wrong because the object pointed to by path=$[0] is not an array.

There is a section describing path_nested and an example in https://identity.foundation/presentation-exchange/spec/v2.0.0/#presentation-submission

But I am not expert on this subject.