Support credential_offer_uri and improve auto-cred-def selection.

CHANGELOG.md

@@ -1,5 +1,13 @@
 # @digitalbazaar/oid4-client Changelog
 
+## 3.7.0 - 2024-08-dd
+
+### Added
+- Add support for fetching credential offer from `credential_offer_uri` via
+  `getCredentialOffer()`.
+- Improve automatic credential definition selection from a credential offer
+  based on the specified `format`.
+
 ## 3.6.0 - 2024-08-22
 
 ### Added

lib/OID4Client.js

@@ -27,7 +27,9 @@ export class OID4Client {
       if(!offer) {
         throw new TypeError('"credentialDefinition" must be an object.');
       }
-      requests = _createCredentialRequestsFromOffer({issuerConfig, offer});
+      requests = _createCredentialRequestsFromOffer({
+        issuerConfig, offer, format
+      });
       if(requests.length > 1) {
         throw new Error(
           'More than one credential is offered; ' +
@@ -48,7 +50,9 @@ export class OID4Client {
   } = {}) {
     const {issuerConfig, offer} = this;
     if(requests === undefined && offer) {
-      requests = _createCredentialRequestsFromOffer({issuerConfig, offer});
+      requests = _createCredentialRequestsFromOffer({
+        issuerConfig, offer, format
+      });
     } else if(!(Array.isArray(requests) && requests.length > 0)) {
       throw new TypeError('"requests" must be an array of length >= 1.');
     }
@@ -393,19 +397,29 @@ function _isPresentationRequired(error) {
   return error.status === 400 && errorType === 'presentation_required';
 }
 
-function _createCredentialRequestsFromOffer({issuerConfig, offer}) {
+function _createCredentialRequestsFromOffer({
+  issuerConfig, offer, format
+}) {
   // get any supported credential configurations from issuer config
   const supported = _createSupportedCredentialsMap({issuerConfig});
 
-  // build requests from credentials identified in `offer`
+  // build requests from credentials identified in `offer` and remove any
+  // that do not match the given format
   const credentials = offer.credential_configuration_ids ?? offer.credentials;
-  return credentials.map(c => {
+  const requests = credentials.map(c => {
     if(typeof c === 'string') {
       // use supported credential config
       return _getSupportedCredentialById({id: c, supported});
     }
     return c;
-  });
+  }).filter(r => r.format === format);
+
+  if(requests.length === 0) {
+    throw new Error(
+      `No supported credential(s) with format "${format}" found.`);
+  }
+
+  return requests;
 }
 
 function _createSupportedCredentialsMap({issuerConfig}) {

lib/index.js

@@ -5,6 +5,7 @@ export * as oid4vp from './oid4vp.js';
 export {
   discoverIssuer,
   generateDIDProofJWT,
+  getCredentialOffer,
   parseCredentialOfferUrl,
   robustDiscoverIssuer,
   signJWT

lib/util.js

@@ -162,6 +162,43 @@ export async function generateDIDProofJWT({
   return signJWT({payload, protectedHeader, signer});
 }
 
+export async function getCredentialOffer({url, agent} = {}) {
+  const {protocol, searchParams} = new URL(url);
+  if(protocol !== 'openid-credential-offer:') {
+    throw new SyntaxError(
+      '"url" must express a URL with the ' +
+      '"openid-credential-offer" protocol.');
+  }
+  const offer = searchParams.get('credential_offer');
+  if(offer) {
+    return JSON.parse(offer);
+  }
+
+  // try to fetch offer from URL
+  const offerUrl = searchParams.get('credential_offer_uri');
+  if(!offerUrl) {
+    throw new SyntaxError(
+      'OID4VCI credential offer must have "credential_offer" or ' +
+      '"credential_offer_uri".');
+  }
+
+  if(!offerUrl.startsWith('https://')) {
+    const error = new Error(
+      `"credential_offer_uri" (${offerUrl}) must start with "https://".`);
+    error.name = 'NotSupportedError';
+    throw error;
+  }
+
+  const response = await fetchJSON({url: offerUrl, agent});
+  if(!response.data) {
+    const error = new Error(
+      `Credential offer fetched from "${offerUrl}" is not JSON.`);
+    error.name = 'DataError';
+    throw error;
+  }
+  return response.data;
+}
+
 export function parseCredentialOfferUrl({url} = {}) {
   assert(url, 'url', 'string');