Issue W3C Credentials (JWT / SD-JWT) via OID4VC

This guide provides a comprehensive walkthrough for issuing a Verifiable Credential based on the W3C standard with a JWT or SD-JWT signature using the walt.id issuer API. The issuance process will utilize the OID4VCI protocol, an extension of OpenID, facilitating secure and standardized communication between identities.

Verifiable Credential (VC): A digital equivalent of physical credentials such as a driver's license or university degree. VCs are cryptographically secure, privacy-respecting, and instantly verifiable.

OID4VCI: A protocol specifying how parties can issue credentials and present them in a way that's consistent and secure across platforms ensuring interoperability.

Setup

See how to access to the issuer API below.

Preparing for Issuance: Key Components

Before issuing a verifiable credential, you'll need:

  1. Raw Credential Data: The information you want to issue as a VC, typically following a specific template or schema.
  2. Signing Key: A cryptographic key used to sign the credential, confirming its authenticity and integrity during verification.

If you don't make any specific configurations, the walt.id issuer API supports different types of W3C credentials which can be found here. If you want to issue other custom credentials, you need to add them to the supported credentials in the issuer metadata. For this example we will issue the by default support Verifiable University Degree, though the process is the same for other credentials.

Example Credential: Verifiable University Degree

{
  // The contextual information required for data integrity and 1.api
  "@context": [
    "https://www.w3.org/2018/credentials/v1",
    "https://www.w3.org/2018/credentials/examples/v1"
  ],
  "id": "http://example.gov/credentials/3732",
  // The credential's unique identifier
  "type": [
    "VerifiableCredential",
    "UniversityDegree"
    // Specifies the kind of credential being issued
  ],
  "issuer": {
    "id": "did:web:vc.transmute.world"
    // The issuer's unique identifier (DID)
  },
  "issuanceDate": "2020-03-10T04:24:12.164Z",
  // When the credential was issued
  "credentialSubject": {
    // Information about the credential's recipient and the degree earned
    "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
    "degree": {
      "type": "BachelorDegree",
      "name": "Bachelor of Science and Arts"
    }
  }
}

Note: Fields like issuer, issuanceDate, and credentialSubject.did are dynamic and will be populated with actual data upon issuance.

Issuing a Credential

In this section, we'll generate a signing key which we store ourselves. For production environments, we recommend using an external KMS provider for key management due to the enhanced security. Learn more about the different types of keys and the storage options here.

Step 1: Get a Signing Key & Issuer DID

As the issuer API doesn't store any cryptographic key material by default. You need to provide the key used for signing the credential in JWK format or a reference object that points to a key stored in an external KMS we support. At the moment, we support Hashicorp Vault and Oracle KMS. In a production environment, we recommend the usage of an external KMS provider to secure the key material.

To create keys and a related DID for signing credentials, you can use the /onboard/issuer endpoint and choose from a variety of algorithms (ed25519, secp256k1, secp256r1, or RSA) and DID methods (did:key, did:jwk, did:web, did:cheqd).

Please refer to our Key Management section to learn more about the different options.

For this guide, we will proceed with generating a JWK ed25519 key and a did:key using the onboard endpoint.

Create Key & DID

CURL

**Endpoint: ** /onboard/issuer | API Reference

Example Request

curl -X 'POST' \
  'http://0.0.0.0:7002/onboard/issuer' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "key": {
    "backend": "jwk",
    "keyType": "secp256r1"
  },
  "did": {
    "method": "jwk"
  }
}'

Body

{
  "key": {
    "backend": "jwk",
    "keyType": "secp256r1"
  },
  "did": {
    "method": "jwk"
  }
}

Body Parameters

  • key
    • backend: String - Specifies the storage type of key. It can be jwk (manged by you), TSE (managed by Hashicorp Vault) and others. Learn more about different types here.
    • keyType: String - the algorithm used to generate the key. For local, it can be ed25519, secp256k1, secp256r1, or RSA. For the other types and the supported algorithms, please go here.
  • did:
    • method: String - Specifies the DID method. It can be key, jwk, web, cheqd.

Example Response

The onboard/issuer endpoint will return an object containing both the generated key in JWK format and the related DID.

{
  "issuerKey": {
    "type": "jwk",
    "jwk": {
      "kty": "OKP",
      "d": "Sr5-oOEXlYU_yCw7ADn-zsvJwMc7cEd2l5klg9i8n1k",
      "crv": "Ed25519",
      "kid": "Zf8NXHGvBlbzX3hdKX1YHZTindNf7LrixPZallJ7nxk",
      "x": "4Iviyx79FlJH5w81DxJwfeRD6JPB4vCJoHzKOQwJ0cs"
    }
  },
  "issuerDid": "did:cheqd:testnet:26948e3c-4493-48fe-a61c-9052ecb62718"
}

As we've used the jwk key type, it's important to note that we need to save the returned values ourselves for future reference. The API doesn't save any information about created keys or DIDs.

Step 2: Issue the Credential

Now, we'll issue a verifiable credential using the key and DID obtained or any other supported JWK. You can choose to either issue the W3C credential as JWT or SD-JWT, which are two different signature types. JWT referring to a JSON-Web-Token and SD-JWT to a Selective-Disclosure JSON Web Token.

Learn more about Selective Disclosure here. In short, it enables your users to only reveal a subset of the claims in a credential to a verifier when suitable. This increases privacy, reduces the risk of identity theft and other types of fraud.

To facilitate the issuance of the credential from us (the issuer) to the holder, we will utilise the OID4VCI protocol. In particular, we will be generating an OID4VC offer URL that can be accepted by any OID compliant wallet to receive credential(s).

The credential offer URL specifies the credentials to be issued. This includes details such as the URL of the issuer, the authorisation and token endpoints, and information about the credential's format, type, and scope.


When we execute the issuance command, two things will happen.

  1. The credential will be signed with the provided key and the chosen signature type (JWT, SD-JWT).
  2. The information about the singed credential will be embedded into the OID Credential Offer URL, which we can send off to our users to claim the credential(s).
JWT
SD-JWT

API Reference

CURL

Endpoint: /openid4vc/jwt/issue

Example Request

curl -X 'POST' \
  'https://issuer.portal.walt.id/openid4vc/jwt/issue' \
  -H 'accept: text/plain' \
  -H 'statusCallbackUri: https://example.com/$id' \
  -H 'Content-Type: application/json' \
  -d '{
  "issuerKey": {
    "type": "jwk",
    "jwk": "{\"kty\":\"OKP\",\"d\":\"mDhpwaH6JYSrD2Bq7Cs-pzmsjlLj4EOhxyI-9DM1mFI\",\"crv\":\"Ed25519\",\"kid\":\"Vzx7l5fh56F3Pf9aR3DECU5BwfrY6ZJe05aiWYWzan8\",\"x\":\"T3T4-u1Xz3vAV2JwPNxWfs4pik_JLiArz_WTCvrCFUM\"}"
  },
  "issuerDid": "did:key:z6MkjoRhq1jSNJdLiruSXrFFxagqrztZaXHqHGUTKJbcNywp",
  "authenticationMethod": "PRE_AUTHORIZED",
  "credentialConfigurationId": "UniversityDegree_jwt_vc_json",
  "credentialData": {
    "@context": [
      "https://www.w3.org/2018/credentials/v1",
      "https://www.w3.org/2018/credentials/examples/v1"
    ],
    "id": "http://example.gov/credentials/3732",
    "type": [
      "VerifiableCredential",
      "UniversityDegree"
    ],
    "issuer": {
      "id": "did:web:vc.transmute.world"
    },
    "issuanceDate": "2020-03-10T04:24:12.164Z",
    "credentialSubject": {
      "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
      "degree": {
        "type": "BachelorDegree",
        "name": "Bachelor of Science and Arts"
      }
    }
  },
  "mapping": {
    "id": "<uuid>",
    "issuer": {
      "id": "<issuerDid>"
    },
    "credentialSubject": {
      "id": "<subjectDid>"
    },
    "issuanceDate": "<timestamp>",
    "expirationDate": "<timestamp-in:365d>"
  }
}'

Header Parameters

  • statusCallbackUri: URL - Receive updates on the created issuance process, e.g. when a credential was successfully claimed. The parameter expects a URL which can accept a JSON POST request. The URL can also hold a $id, which will be replaced by the issuance session id. For example: https://myurl.com/$id, https://myurl.com or https://myurl.com/test/$id

    Expand To Learn More

    Body

    The data send to the provided URL will contain a JSON body:

    • id : String - the issuance session id
    • type: String - the event type
    • data: JsonObject - the data for the event

    Event Types

    Possible events (event types) and their data are:

    • resolved_credential_offer with the credential offer as JSON (in our Web Wallet: called when the issuance offer is entered into the wallet, but not processing / accepted yet)
    • requested_token with the issuance request for the token as json object (called for the token required to receive the credentials)

    Credential issuance (called for every credential that's issued (= requested from wallet))

    • jwt_issue with jwt being the issued jwt
    • sdjwt_issue with sdjwt being the issued sdjwt
    • batch_jwt_issue with jwt being the issued jwt
    • batch_sdjwt_issue with sdjwt being the issued sdjwt
    • generated_mdoc with mdoc being the CBOR (HEX) of the signed mdoc

    To allow for secure business logic flows, if a callback URL is set, and it cannot be reached, the issuance will not commence further (after that point). If no callback URL is set, the issuance logic does not change in any way.

Body

{
  "issuerKey": {
    "type": "jwk",
    "jwk": "{\"kty\":\"OKP\",\"d\":\"mDhpwaH6JYSrD2Bq7Cs-pzmsjlLj4EOhxyI-9DM1mFI\",\"crv\":\"Ed25519\",\"kid\":\"Vzx7l5fh56F3Pf9aR3DECU5BwfrY6ZJe05aiWYWzan8\",\"x\":\"T3T4-u1Xz3vAV2JwPNxWfs4pik_JLiArz_WTCvrCFUM\"}"
  },
  "issuerDid": "did:key:z6MkjoRhq1jSNJdLiruSXrFFxagqrztZaXHqHGUTKJbcNywp",
  "credentialConfigurationId": "UniversityDegree_jwt_vc_json",
  "credentialData": {
    "@context": [
      "https://www.w3.org/2018/credentials/v1",
      "https://www.w3.org/2018/credentials/examples/v1"
    ],
    "id": "http://example.gov/credentials/3732",
    "type": [
      "VerifiableCredential",
      "UniversityDegree"
    ],
    "issuer": {
      "id": "did:web:vc.transmute.world"
    },
    "issuanceDate": "2020-03-10T04:24:12.164Z",
    "credentialSubject": {
      "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
      "degree": {
        "type": "BachelorDegree",
        "name": "Bachelor of Science and Arts"
      }
    }
  },
  "mapping": {
    "id": "<uuid>",
    "issuer": {
      "id": "<issuerDid>"
    },
    "credentialSubject": {
      "id": "<subjectDid>"
    },
    "issuanceDate": "<timestamp>",
    "expirationDate": "<timestamp-in:365d>"
  },
  "authenticationMethod": "PRE_AUTHORIZED",
  "standardVersion": "DRAFT13"
}

Body Parameters

  • issuerKey: JSON - A JWK or reference object to a key stored in an external KMS to sign the credential with. Supported algorithms: ed25519, secp256k1, secp256r1, or RSA.
    JWK Format: {"type": "jwk", "jwk": Here JSON Web Key Object}. Can be provided as String Or JWK object to " issuerKey".
    KMS Key: Please refer to the Key Management Section and the KMS you want to use for more details on the structure of the reference object.
  • issuerDid: String - The DID related to the provided key.
  • credentialConfigurationId: String - Reference to a specific credential configuration the issuer supports. As our issuer currently supports W3C JWT & SD-JWT credentials and SD-JWT VCs (IETF). The structure of the credentialConfigurationId is the following: " credentialType_jwt_vc_json" for W3C JWT & SD-JWT credentials and "credentialType_vc+sd-jwt" for SD-JWT VCs (IETF). E.g. "UniversityDegree_jwt_vc_json" or " UniversityDegree_vc+sd-jwt". You can also view the credentialConfigurationIds by visiting the /.well-known/openid-credential-issuer endpoint of your issuer. The metadata of our deployed issuer for testing can be seen here.
  • credentialData: JSON - A credential data structure to sign (W3C compliant). A list of predefined valid structures can be found here.
  • mapping (optional): JSON - The mapping object that allows for dynamic value insertion via data functions, executed at the time when the credentials is claimed. This feature enables personalized credentials based on real-time data. Learn more about it and see a list of supported data functions here.
  • standardVersion: (optional) String - Defines which OIDC4VCI standard version is used. The supported standard versions are: DRAFT13 and DRAFT11. If no value is provided, it will default to DRAFT13.
  • authenticationMethod: (optional) String - Defines which OIDC4VC exchange flow is used (pre-auth or full-auth). If no value is provided, it will default to pre-auth flow indicated as PRE_AUTHORIZED. The parameter options are:
Expand To Learn More About The Options
  • PWD - used for authorization code flow with username/password authentication with external auth server
  • ID_TOKEN - used for authorization code flow with id_token authentication. When this method is used an authorization request is sent to the wallet, which generates and issues the ID_TOKEN using its DID ( Decentralized Identifier). The issuer then verifies the ID_TOKEN to confirm the holder's identity and DID.
  • VP_TOKEN - used for authorization code flow with vp_token(OIDC4VP). With this method, the receiver of the credential must be authenticated by presenting the requested credential. The credential which must be presented can be configured using the vpRequestedValue as explained below. The policies which are applied to the presented credential are 'signature,' 'expired,' and 'not-before.' Learn more about policies here.
  • NONE - used for authorization code flow with none authentication method
  • PRE_AUTHORIZED - used for pre-authorizated code flow

Additional parameters required for selected auth method:

For "ID_TOKEN" and "VP_TOKEN":

  • useJar: (Optional) Boolean - used for using JAR OAuth specification in the id/vp_token requests. If omitted, the default value is true.

For VP_TOKEN:

  • vpRequestedValue: String - Specifies the requested credential type value for the VP token. E.g. "VerifiableId"
  • vpProfile: (Optional) String - Specifies the profile of the VP request. Available Profiles: DEFAULT: For W3C OpenID4VP, ISO_18013_7_MDOC: For MDOC OpenID4VP, EBSIV3: For EBSI V3 Compliant VP. If omitted, the default value is DEFAULT

Example Response

The issuer endpoint will respond with Credential Offer URL.

Plain Response

openid-credential-offer://issuer.portal.walt.id/?credential_offer=%7B%22credential_issuer%22%3A%22https%3A%2F%2Fissuer.portal.walt.id%22%2C%22credentials%22%3A%5B%7B%22format%22%3A%22jwt_vc_json%22%2C%22types%22%3A%5B%22VerifiableCredential%22%2C%22UniversityDegree%22%5D%2C%22credential_definition%22%3A%7B%22%40context%22%3A%5B%22https%3A%2F%2Fwww.w3.org%2F2018%2Fcredentials%2Fv1%22%2C%22https%3A%2F%2Fwww.w3.org%2F2018%2Fcredentials%2Fexamples%2Fv1%22%5D%2C%22types%22%3A%5B%22VerifiableCredential%22%2C%22UniversityDegree%22%5D%7D%7D%5D%2C%22grants%22%3A%7B%22authorization_code%22%3A%7B%22issuer_state%22%3A%220431b78c-cd94-4f50-bfdf-e24d436c0cf6%22%7D%2C%22urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Apre-authorized_code%22%3A%7B%22pre-authorized_code%22%3A%22eyJhbGciOiJFZERTQSJ9.eyJzdWIiOiIwNDMxYjc4Yy1jZDk0LTRmNTAtYmZkZi1lMjRkNDM2YzBjZjYiLCJpc3MiOiJodHRwczovL2lzc3Vlci5wb3J0YWwud2FsdC5pZCIsImF1ZCI6IlRPS0VOIn0.NorG7GtjmA-HXMJfUzU9vfnshcIgFY0oYQb8qJjDfORPoNxuurgySSOIDKFi7Z4XJmC-oJZnM0Nbb0NUd57cDA%22%2C%22user_pin_required%22%3Afalse%7D%7D%7D

Decoded

openid-credential-offer://issuer.portal.walt.id/?
credential_offer=
{
  "credential_issuer": "https://issuer.portal.walt.id",
  "credentials": [
    {
      "format": "jwt_vc_json",
      "types": [
        "VerifiableCredential", 
        "UniversityDegree"
      ],
      "credential_definition": {
        "@context": [
          "https://www.w3.org/2018/credentials/v1", 
          "https://www.w3.org/2018/credentials/examples/v1"
        ],
        "types": [
          "VerifiableCredential", 
          "UniversityDegree"
        ]
      }
    }
  ],
  "grants": {
    "authorization_code": {
      "issuer_state": "0431b78c-cd94-4f50-bfdf-e24d436c0cf6"
    },
    "urn:ietf:params:oauth:grant-type:pre-authorized_code": {
      "pre-authorized_code": "eyJhbGciOiJFZERTQSJ9.eyJzdWIiOiIwNDMxYjc4Yy1jZDk0LTRmNTAtYmZkZi1lMjRkNDM2YzBjZjYiLCJpc3MiOiJodHRwczovL2lzc3Vlci5wb3J0YWwud2FsdC5pZCIsImF1ZCI6IlRPS0VOIn0.NorG7GtjmA-HXMJfUzU9vfnshcIgFY0oYQb8qJjDfORPoNxuurgySSOIDKFi7Z4XJmC-oJZnM0Nbb0NUd57cDA",
      "user_pin_required": false
    }
  }
}

Step 3: Receive the Credential Offer

The created credential offer can now be embedded into a QR code for users to scan with their mobile wallet or pasted manually into the credential offer field of our web wallet.

Try It Out: Use our web wallet for a practical demonstration. After logging in, click the 'request credential' button and paste the received Offer URL into the text field below the camera.

🎉 Congratulations, you've issued a W3C-compliant Verifiable Credential using OID4VCI! 🎉

Azure Key VaultIssue SD-JWT VC Credentials via OID4VC