Add optimization for controller docs that are DID docs.

Author: dlongley

CHANGELOG.md

@@ -1,5 +1,13 @@
 # jsonld-signatures ChangeLog
 
+## 9.3.0 - 2021-07-xx
+
+### Added
+- Add optimization for JSON-LD controller documents that are DID documents. When
+  a controller ID resolves to a JSON-LD DID Document, then JSON-LD framing can
+  be skipped when verifying verification method relationships if the verification
+  relationship is one that is defined by the DID context.
+
 ## 9.2.1 - 2021-07-08
 
 ### Fixed

lib/purposes/ControllerProofPurpose.js

@@ -7,6 +7,18 @@ const constants = require('../constants');
 const jsonld = require('jsonld');
 const ProofPurpose = require('./ProofPurpose');
 
+// DID documents can be specially optimized
+const DID_CONTEXT_V1 = 'https://www.w3.org/ns/did/v1';
+// verification relationship terms that are known to appear in DID documents
+const DID_VR_TERMS = [
+  'assertionMethod',
+  'authentication',
+  'capabilityInvocation',
+  'capabilityDelegation',
+  'keyAgreement',
+  'verificationMethod'
+];
+
 module.exports = class ControllerProofPurpose extends ProofPurpose {
   /**
    * Creates a proof purpose that will validate whether or not the verification
@@ -30,6 +42,7 @@ module.exports = class ControllerProofPurpose extends ProofPurpose {
       }
       this.controller = controller;
     }
+    this._termDefinedByDIDContext = DID_VR_TERMS.includes(term);
   }
 
   /**
@@ -57,6 +70,7 @@ module.exports = class ControllerProofPurpose extends ProofPurpose {
       }
 
       const {id: verificationId} = verificationMethod;
+      const {term, _termDefinedByDIDContext} = this;
 
       // if no `controller` specified, use verification method's
       if(this.controller) {
@@ -75,23 +89,31 @@ module.exports = class ControllerProofPurpose extends ProofPurpose {
           }
         }
 
-        // Note: `expansionMap` is intentionally not passed; we can safely drop
-        // properties here and must allow for it
-        const framed = await jsonld.frame(controllerId, {
-          '@context': constants.SECURITY_CONTEXT_URL,
-          id: controllerId,
-          // the term should be in the json-ld object the controllerId resolves
-          // to.
-          [this.term]: {
-            '@embed': '@never',
-            id: verificationId
-          }
-        }, {documentLoader, compactToRelative: false});
-        result.controller = framed;
+        // apply optimization to controller documents that are DID documents;
+        // if `term` is one of those defined by the DID context
+        let {document} = await documentLoader(controllerId);
+        const mustFrame = !(_termDefinedByDIDContext &&
+          document['@context'] === DID_CONTEXT_V1 ||
+          (Array.isArray(document['@context']) &&
+          document['@context'][0] === DID_CONTEXT_V1));
+        if(mustFrame) {
+          // Note: `expansionMap` is intentionally not passed; we can safely
+          // drop properties here and must allow for it
+          document = await jsonld.frame(document, {
+            '@context': constants.SECURITY_CONTEXT_URL,
+            id: controllerId,
+            // this term must be in the JSON-LD controller document or
+            // verification will fail
+            [term]: {
+              '@embed': '@never',
+              id: verificationId
+            }
+          }, {documentLoader, compactToRelative: false});
+        }
+        result.controller = document;
       }
 
-      const verificationMethods = jsonld.getValues(
-        result.controller, this.term);
+      const verificationMethods = jsonld.getValues(result.controller, term);
       result.valid = verificationMethods.some(vm =>
         vm === verificationId ||
         (typeof vm === 'object' && vm.id === verificationId));