mandate issuance of batches of the credentials

[Sakurann]

batch endpoint has been removed in #196, but i think we still need text in HAIP that mandates support for batch issuance using credential endpoint.

probably no need to say that explicitly, but once we will have ZKP, HAIP for ZKP won't mandate batch issuance anymore, but since for the current HAIP, only mdoc and sd-jwt vc are in scope, so mandating batch issuance makes sense :)

[jogu]

Discussed on today's WG call:

Whether batch issuance is used or not is likely to be issuer policy.

If batch_credential_issuance is present in the issuer metadata, this is an indication to the wallet that all credentials from this issuer issues credentials that could be vulnerable to verifier-verifier linkability. The tone should match the existing text:

Note: Re-using the same Credential across Verifiers, or re-using the same JWK value across multiple Credentials gives colluding Verifiers a mechanism to correlate the User. There are currently two known ways to address this with SD-JWT VCs. First is to issue multiple instances of the same Credentials with different JWK values, so that if each instance of the Credential is used at only one Verifier, it can be reused multiple times. Another is to use each Credential only once (ephemeral Credentials). It is RECOMMENDED to adopt one of these mechanisms.

Kristina to propose text.

[Sakurann]

this is related but not directly related to this issue: note quoted in Joseph's comment does not really belong in haip, since we already have detailed sections on this topic in VP and VCI. proposing to paraphrase it to the following:

Note: How to prevent correlations by colluding Issuer/Verifier or Verifier/Verifier pairs, or by the same Verifier, see Section 15.4.1 in [@!OIDF.OID4VCI] and Section 15.5 in [@!OIDF.OID4VP].