Use different custom schemes for credential offer and presentation

[GarethCOliver]

Currently haip:// is being mandated for both credential offer and presentation. We should distinguish, to make it easier to register for only one (i.e. register only for credential offers and not presentations if a wallet has no credentials available).

This is particularly important due to the poor (or non-functional) experience when multiple apps are registered to the same custom scheme.

[awoie]

I would argue to not use custom schemes at all, see #244 and accept the issue in HAIP that we cannot solve NASCAR. This is why we have DC API.

[Sakurann]

to the original issue, I agree it is cleaner to have different custom url schemes for presentation and issuance.

to Oliver's comment that is related but somewhat different topic, OpenID4VP/VCI over DC API is not supported by one of the major platforms and as an implementer, i do not want to be held hostage to the decision of that company for the flows to work. so as much as I understand the limitation of custom url schemes, i would not want to drop it, at least until/unless openid4vp/vci over DC API works seamlessly across major platforms.

[Sakurann]

wg discussion:

• conditional to wg agreeing to use custom schemes for credential offer and presentation, it is reasonable to separate values used for issuance and presentation. haip-vp:// and haip-vci:// or something? (feel free to suggest alternatives)