Add example how to use ISO mdoc and SD-JWT VC in one request and response

[awoie]

We should add an example to OID4VP on how to combine the ISO mdoc and SD-JWT VC format. The example should cover request and response payloads. The following use cases should be demonstrated:

• the same credential type in two different formats, so the wallet can choose which format to pick (some issuer might choose to not do dual issuance)
• two different credential types in two different formats where both credential types should be included in the response

[tlodderstedt]

Can you shed some light on the use case? I see use cases for requesting a credential in two formats for issuance, I would like to understand why a verifier would request the presentation of the same credential in different formats.

[awoie]

Use case is that as an RP I don't know which PID format the wallet supports, so I request a PID in different formats to increase my chance the wallet has a match.

[babisRoutis]

@awoie Totally agree.

If I am not mistaken, currently there is an example (of case 2) where a W3C VC DM and an SD-JWT-VC are returned in a vp_token. It would be great if we could have this also for mso_mdoc + SD-JWT-VC and especially the 2nd case.

People reading the ISO18013-7 or/and ISO23220-4 , as OpenId4VP suggests, may get the impression that vp_token is always a string. It would be helpful if we could have an indicative example where vp_token (in two different types/formats) is a JSON array and the related presentation_submission.

Lately, I came across also in other, perhaps related, issue:

How to respond in a presentation definition, asking for two different documents, both in mso_mdoc. Some return a string vp_token representing a device response with two documents and others a JSON array vp_token comprised two different strings.

[Sakurann]

Please go ahead and do a PR with an example, @awoie or @babisRoutis. we might be able to put it in ID, as an editorial change during the review period