feat: adds support for providing a proofDocument with multiple proofs

see issue #79 for details

__tests__/deriveProof.spec.ts

@@ -16,11 +16,16 @@ import {
   testSignedDocument,
   customLoader,
   testSignedVcDocument,
-  testRevealVcDocument
+  testRevealVcDocument,
+  testSignedDocumentMultiProofs,
+  testSignedDocumentMultiDifProofs,
+  testSignedDocumentEd25519
 } from "./__fixtures__";
 
 import { BbsBlsSignatureProof2020, deriveProof } from "../src/index";
 
+import jsigs from "jsonld-signatures";
+
 describe("BbsBlsSignatureProof2020", () => {
   it("should derive proof", async () => {
     const result = await deriveProof(testSignedDocument, testRevealDocument, {
@@ -49,4 +54,78 @@ describe("BbsBlsSignatureProof2020", () => {
     );
     expect(result).toBeDefined();
   });
+
+  it("should derive proofs from a document featuring multiple supporting proofs", async () => {
+    const result = await deriveProof(
+      testSignedDocumentMultiProofs,
+      testRevealDocument,
+      {
+        suite: new BbsBlsSignatureProof2020(),
+        documentLoader: customLoader
+      }
+    );
+    expect(result).toBeDefined();
+    expect(result.proof.length).toBe(2);
+  });
+
+  it("should derive proofs from a document featuring multiple different proofs with at least 1 supporting proof", async () => {
+    const result = await deriveProof(
+      testSignedDocumentMultiDifProofs,
+      testRevealDocument,
+      {
+        suite: new BbsBlsSignatureProof2020(),
+        documentLoader: customLoader
+      }
+    );
+    expect(result).toBeDefined();
+
+    // this returns a document with only a single proof so it should be an object rather than an array
+    expect(Array.isArray(result.proof)).toBe(false);
+  });
+
+  it("should derive proofs from multiple proof documents and be able to verify them using jsonld-signatures library", async () => {
+    const result = await deriveProof(
+      testSignedDocumentMultiProofs,
+      testRevealDocument,
+      {
+        suite: new BbsBlsSignatureProof2020(),
+        documentLoader: customLoader,
+        skipProofCompaction: false
+      }
+    );
+
+    const derivedProofVerified = await jsigs.verify(result, {
+      suite: new BbsBlsSignatureProof2020(),
+      purpose: new jsigs.purposes.AssertionProofPurpose(),
+      documentLoader: customLoader
+    });
+
+    expect(result).toBeDefined();
+    expect(result.proof.length).toBe(2);
+    expect(derivedProofVerified.verified).toBeTruthy();
+  });
+
+  it("should throw an error when proofDocument is the wrong type", async () => {
+    await expect(
+      deriveProof(
+        [testSignedDocument, testSignedDocument],
+        testRevealDocument,
+        {
+          suite: new BbsBlsSignatureProof2020(),
+          documentLoader: customLoader
+        }
+      )
+    ).rejects.toThrowError("proofDocument should be an object not an array.");
+  });
+
+  it("should throw an error when proofDocument doesn't include a BBSBlsSignatureProof2020", async () => {
+    await expect(
+      deriveProof(testSignedDocumentEd25519, testRevealDocument, {
+        suite: new BbsBlsSignatureProof2020(),
+        documentLoader: customLoader
+      })
+    ).rejects.toThrowError(
+      "There were not any BBSBlsSignatureProof2020 proofs provided that can be used to derive a proof."
+    );
+  });
 });

src/deriveProof.ts

@@ -34,36 +34,69 @@ export const deriveProof = async (
     throw new TypeError('"options.suite" is required.');
   }
 
+  if (Array.isArray(proofDocument)) {
+    throw new TypeError("proofDocument should be an object not an array.");
+  }
+
   const { proofs, document } = await getProofs({
     document: proofDocument,
     proofType: suite.supportedDeriveProofType,
     documentLoader,
     expansionMap
   });
 
-  const result = await suite.deriveProof({
+  if (proofs.length === 0) {
+    throw new Error(
+      "There were not any BBSBlsSignatureProof2020 proofs provided that can be used to derive a proof."
+    );
+  }
+  let derivedProof;
+
+  derivedProof = await suite.deriveProof({
     document,
     proof: proofs[0],
     revealDocument,
     documentLoader,
     expansionMap
   });
 
+  if (proofs.length > 1) {
+    // convert the proof property value from object ot array of objects
+    derivedProof = { ...derivedProof, proof: [derivedProof.proof] };
+
+    // drop the first proof because it's already been processed
+    proofs.splice(0, 1);
+
+    // add all the additional proofs to the derivedProof document
+    for (const proof of proofs) {
+      const additionalDerivedProofValue = await suite.deriveProof({
+        document,
+        proof,
+        revealDocument,
+        documentLoader,
+        expansionMap
+      });
+      derivedProof.proof.push(additionalDerivedProofValue.proof);
+    }
+  }
+
   if (!skipProofCompaction) {
     /* eslint-disable prefer-const */
     let expandedProof: any = {
-      [SECURITY_PROOF_URL]: { "@graph": result.proof }
+      [SECURITY_PROOF_URL]: {
+        "@graph": derivedProof.proof
+      }
     };
 
     // account for type-scoped `proof` definition by getting document types
-    const { types, alias } = await getTypeInfo(result.document, {
+    const { types, alias } = await getTypeInfo(derivedProof.document, {
       documentLoader,
       expansionMap
     });
 
     expandedProof["@type"] = types;
 
-    const ctx = jsonld.getValues(result.document, "@context");
+    const ctx = jsonld.getValues(derivedProof.document, "@context");
 
     const compactProof = await jsonld.compact(expandedProof, ctx, {
       documentLoader,
@@ -74,13 +107,22 @@ export const deriveProof = async (
     delete compactProof[alias];
     delete compactProof["@context"];
 
+    /**
+     * removes the @included tag when multiple proofs exist because the
+     * @included tag messes up the canonicalized bytes leading to a bad
+     * signature that won't verify.
+     **/
+    if (compactProof.proof["@included"]) {
+      compactProof.proof = compactProof.proof["@included"];
+    }
+
     // add proof to document
     const key = Object.keys(compactProof)[0];
-    jsonld.addValue(result.document, key, compactProof[key]);
+    jsonld.addValue(derivedProof.document, key, compactProof[key]);
   } else {
-    delete result.proof["@context"];
-    jsonld.addValue(result.document, "proof", result.proof);
+    delete derivedProof.proof["@context"];
+    jsonld.addValue(derivedProof.document, "proof", derivedProof.proof);
   }
 
-  return result.document;
+  return derivedProof.document;
 };