Implement Ethereum Controller Credential using DIDKit

[clehner]

Depends on: spruceid/ssi#99, spruceid/didkit#82

This implements credential issuance using DIDKit and MetaMask for the Ethereum Controller Credential. The credential is implemented using sameAs, as shown in https://gist.github.com/tplooker/ca8c147906764afb26d95170900c560c. The issuer is the user's MetaMask identity, using the prototype Eip712Method2021 added in spruceid/ssi#99.

DIDKit and ssi are added to the readme dependencies to be cloned alongside this repo. The package.json is updated to point to DIDKit's WASM package, and a symlink is added in public/ to point to the WASM file.

Not yet implemented:

• Getting the user's DID where they will store the credential
• Offering the credential to the user using CHAPI - Done in b730d3f
• License disclosures, attributions and copyright notices for DIDKit: List licenses of dependencies for binary releases didkit#77 (Also should probably be added for this project and its npm dependencies)

Screenshots

Obsolete screenshot

This screenshot is superceded by the one in #7 (comment) as implemented in b730d3f.

[clehner]

Updated to save the issued credential to a CHAPI wallet using credential-handler-polyfill rather than putting the JSON in the page. Also added the option to download it as a file.

[wyc]

@clehner is this good to review?

[clehner]

@wyc yes. It just doesn't yet identify the user's DID for the credential subject - but that can be added separately.