Linked Verifiable Presentations

[daniel-mader]

Description of change

Adds support for Linked Verifiable Presentations following this DIF specification.
Implementation follows the existing linked_domain_service.rs.

Links to any relevant issues

n/a

Type of change

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• Bug fix (a non-breaking change which fixes an issue)
• Enhancement (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Fix

How the change has been tested

• automated unit tests
• manual exploration testing

Change checklist

Add an x to the boxes that are relevant to your changes.

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[UMR1352]

Hi @daniel-mader, thanks for submitting this. @eike-hass told me you had some concerns regarding the resolution of LinkedVerifiablePresentations as well as the development of WASM bindings for this feature.

As we have done in other instances, we won't provide direct support for resolving LinkedVerifiablePresentations unless hosted on the Tangle (which we don't support yet but we might in the future). Users though should still be able to resolve them manually.

For the latter matter, we will take care of the bindings as well as making sure CI won't complain about the code before merging it.

[daniel-mader]

Hey @UMR1352, thanks for your feedback! Regarding the resolution, my questions revolve around whether we should check if the link is valid at all or if we should completely treat it as some arbitrary URL and not even check if the resource can be fetched or not. Shall I also guide the user how to create a VP (without nonce) to be hosted or rather add a reference to the existing example?

[UMR1352]

Checking if the URL are fetchable would require resolution of the resource. I think we could simply stick to checking for its syntactic validity.
If you feel like expanding the example that would be great but it's not strictly necessary for the approval of this PR.