[Task] Implement new Resolver API

[JelleMillenaar]

Description

Old Description: As has been discussed at length in discussion #422, the Resolver logic will be completely refactored with a new API design. It will be able to internally cache the DID message data from the Tangle and return metadata. An additional DID spec compliant API will be introduced in a later issue.

New Description: We have discussed a new Resolver API, that crates a consistent object that can be used for Verification throughout an application. It works for multiple resolutions, may work with multiple networks (main, dev, shimmer) and can resolve different methods (iota, stardust?, disposable?). The same Verifier API can also take care of VC and VP verification. DID resolution and VC & VP verification may be done with resolution/verification options such as resolve_at or verifiy_at. Caching is out of scope for this PR.

For details about the API design, I'd refer to #422 and the comments on this Issue.

Motivation

Improve developer experience with a clean, easy yet powerful API.

To-do list

Create a task-specific to-do list . Please link PRs that match the To-do list item behind the item after it has been submitted.

• Implement new API
  • Partially addressed in Replace ClientMap with new Resolver #594
• Update Examples
  • Requires Overhaul CredentialValidator, add PresentationValidator #599

[cycraig]

As per internal discussions and #422, using the initial resolver API might look something like the following:

// A Resolver should either contain a ClientMap or it could replace it entirely.
let client_map = ClientMap::new().await;
client_map.insert(Client::from_network(Network::Devnet).await?);

// Build a resolver that caches calls to the tangle for this specific did
let resolver = Resolver::new(client_map);

// Resolve the latest version of a DID document (basically the same as Client::resolve right now),
// where IotaTangleDocument is a new wrapper struct from the metadata refactor.
let iota_did: IotaDID = "did:iota:...".parse().unwrap();
let document: IotaTangleDocument = resolver.resolve(&iota_did).await?;

// Try resolve a DID document from a specific version.
let old_document: IotaTangleDocument = resolver.resolve_with_options(
  &iota_did, 
  ResolveOptions::new().version_id("1.5")
).await?;

// Try resolve a DID document from a specific timestamp.
let old_document: IotaTangleDocument = resolver.resolve_with_options(
  &iota_did, 
  ResolveOptions::new().version_time("2021-10-01T00:00:00Z")
).await?;

// Separate API, but can share the network cache of the created resolver instance.
let history: DocumentHistory = resolver.resolve_history(&iota_did).await?;

// Verify a presentation or credential, fetching issuer and subject DID documents automatically.
let validation: PresentationValidation = resolver.verify_presentation(&presentation).await?;
let validation: CredentialValidation = resolver.verify_credential(&credential).await?;

The exact details of each method are still unclear at this stage. Since ResolveOptions is a bit unwieldy and allows conflicting options (version_time and version_id seem incompatible), we could a builder pattern similar to what was originally suggested in #422.

E.g.

// Resolve the latest version of a DID document with default options.
let document: IotaTangleDocument = resolver.resolve(&iota_did).fetch().await?;

// Resolve a specific version of a DID document.
let old_document: IotaTangleDocument = resolver.resolve(&iota_did)
  .version_id("1.5")
  .fetch()
  .await?;

[cycraig]

The Resolver design is kind of blocked by uncertainty at the moment. While implemented, it lacks features to resolve specific points in time (due to uncertainty around whether the full history will always be available), or versions (versioning is not implemented yet for the same reason). Resolving across different networks is supported by not across different methods (because how those methods will be implemented technically in Rust is also still uncertain).

I feel like this issue can be closed and new ones opened to extend the Resolver with extra functionality as-needed.

[cycraig]

Closed by #594.

See above comment #493 (comment).