Add a way to check what protocols are supported

[marcoscaceres]

trafficstars

It's currently not possible to check what protocols the browser supports so developers won't know if calling .get() will immediately fail (as it requires user activation).

As such, we should then add a. static setlike.supportedProtocols With the sequence, a developer can easily filter with standard Set methods.

Proposed API addition

interface DigitalCredentialsSupportedProtocols {
  readonly setlike<DOMString>; // user agent pre-populates
};

partial interface DigitalCredential {
   readonly attribute DigitalCredentialsSupportedProtocols supportedProtocols;
}

Usage:

if (DigitalCredential.supportedProtocols.has("openid4vp")) {
  // let's make an openid4vp request
}

// Or you can do...
const supported = Array.from(DigitalCredential.supportedProtocols).filter(typesTheRPSupports);

// Or whatever developers want:
for (const supported in DigitalCredential.supportedProtocols.values()) {
   // do things with supported
}

const requests = [...DigitalCredential.supportedProtocols].map(toRequestWeKnowHowToMake);

// or even... 
switch (true) {
   case DigitalCredential.supportedProtocols.has("openid4vp"):
      makeOpenIDRequest(data);
      break;
   case DigitalCredential.supportedProtocols.has("whatever"):
      makeWhateverRequest(data);
      break;
   default:
     throw TypeError("Oh noes! they don't support our favorite protocol!")
}

That gives a ton of flexibility. You can even use it will all the new fancy JavaScript set comparison operations:

// DigitalCredential.supportedProtocols is a Set
const supportedProtocols = DigitalCredential.supportedProtocols;

// Example Set of protocols to compare
const protocolsToCheck = new Set(['openid4vp', 'someOtherProtocol']);

// Union: Combining both sets
const union = supportedProtocols.union(protocolsToCheck);
console.log(union); // Set { 'openid4vp', 'someOtherProtocol', ... }

// Intersection: Getting common protocols between the sets
const intersection = supportedProtocols.intersection(protocolsToCheck);
console.log(intersection); // Set { 'openid4vp' }

// Difference: Getting protocols supported by DigitalCredential but not in protocolsToCheck
const difference = supportedProtocols.difference(protocolsToCheck);
console.log(difference); // Set { ... } (protocols supported by DigitalCredential but not in protocolsToCheck)

// Symmetric Difference: Getting protocols that are in either set, but not in both
const symmetricDifference = supportedProtocols.symmetricDifference(protocolsToCheck);
console.log(symmetricDifference); // Set { 'someOtherProtocol', ... }