feat: Add credentialSchema attribute (eclipse-dataspace-dcp#201)

* Add credentialSchema attribute

* Update specifications/credential.issuance.protocol.md

Co-authored-by: Arno Weiß <86715435+arnoweiss@users.noreply.github.com>

---------

Co-authored-by: Arno Weiß <86715435+arnoweiss@users.noreply.github.com>

Author: jimmarino

artifacts/src/main/resources/context/dcp.jsonld

@@ -47,6 +47,9 @@
         "credentialType": {
           "@id": "dcp:credentialType"
         },
+        "credentialSchema": {
+          "@id": "dcp:credentialSchema"
+        },
         "offerReason": {
           "@id": "dcp:offerReason",
           "@type": "xsd:string"

artifacts/src/main/resources/issuance/credential-object-schema.json

@@ -15,6 +15,9 @@
         "credentialType": {
           "type": "string"
         },
+        "credentialSchema": {
+          "type": "string"
+        },
         "offerReason": {
           "type": "string"
         },

artifacts/src/main/resources/issuance/example/credential-object.json

@@ -4,6 +4,7 @@
   ],
   "type": "CredentialObject",
   "credentialType": "CompanyCredential",
+  "credentialSchema": "https://example.com/credentials/credentialSchema",
   "offerReason": "reissue",
   "bindingMethods": [
     "did:web"

artifacts/src/test/java/org/eclipse/dcp/schema/issuance/CredentialObjectSchemaTest.java

@@ -27,6 +27,7 @@ public class CredentialObjectSchemaTest extends AbstractSchemaTest {
             {
                 "type": "CredentialObject",
                 "credentialType": "VerifiableCredential",
+                "credentialSchema": "https://example.com/credentials/credentialSchema",
                 "offerReason": "reissue",
                 "bindingMethods": [
                   "did:web"

specifications/credential.issuance.protocol.md

@@ -231,9 +231,10 @@ The following is a non-normative example of a credential offer request:
 |--------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | **Schema**   | [JSON Schema](./resources/issuance/credential-object-schema.json)                                                                                                                                                             |
 | **Required** | - `type`: A string specifying the `CredentialObject` type                                                                                                                                                                     |
-|              | - `credentialType`: A single string specifying type of credential being offered                                                                                                                                         |
+|              | - `credentialType`: A single string specifying type of credential being offered                                                                                                                                               |
 | **Optional** | - `@context`: Specifies a valid Json-Ld context ([[json-ld11]], sect. 3.1). As the `credentialObject` is usually embedded, its context is provided by the enveloping object.                                                  |
 |              | - `bindingMethods`: An array of strings defining the key material that an issued credential is bound to                                                                                                                       |
+|              | - `credentialSubject`: A URL pointing to the credential schema of the object in a VC's `credentialSubject` property.|
 |              | - `profiles`: An array of strings containing the aliases of the [profiles](#profiles-of-the-decentralized-claims-protocol), e.g. `"vc20-bssl/jwt"`                                                                            |
 |              | - `issuancePolicy`: A [presentation definition](https://identity.foundation/presentation-exchange/spec/v2.0.0/#presentation-definition) [[presentation-ex]] signifying the required [=Verifiable Presentation=] for issuance. |
 |              | - `offerReason`: A reason for the offer as a string. Valid values may include `reissue` and `proof-key-revocation`                                                                                                            |