EUDI OpenId4VCI library

❗ Important! Before you proceed, please read the EUDI Wallet Reference Implementation project description

Table of contents

• Overview
• Disclaimer
• How to use
• Features supported
• How to contribute
• License

Overview

This is a Swift library, that supports the OpenId4VCI (draft 14) protocol. In particular, the library focuses on the wallet's role in the protocol to:

• Resolve credential issuer metadata
• Resolve metadata of the authorization server protecting issuance services
• Resolve a credential offer presented by an issuer service
• Negotiate authorization of a credential issuance request
• Submit a credential issuance request

Disclaimer

The released software is an initial development release version:

• The initial development release is an early endeavor reflecting the efforts of a short timeboxed period, and by no means can be considered as the final product.
• The initial development release may be changed substantially over time, might introduce new features but also may change or remove existing ones, potentially breaking compatibility with your existing code.
• The initial development release is limited in functional scope.
• The initial development release may contain errors or design flaws and other problems that could cause system or other failures and data loss.
• The initial development release has reduced security, privacy, availability, and reliability standards relative to future releases. This could make the software slower, less reliable, or more vulnerable to attacks than mature software.
• The initial development release is not yet comprehensively documented.
• Users of the software must perform sufficient engineering and additional testing in order to properly evaluate their application and determine whether any of the open-sourced components is suitable for use in that application.
• We strongly recommend to not put this version of the software into production use.
• Only the latest version of the software will be supported

How to use

The library provides the following main api elements to facilitate consumers of this api with the operations related to verifiable credentials issuance

• Metadata resolvers: Components that interact with a credential issuer and its authorization server to obtain and parse their metadata.
• Credential offer resolver: A component that interacts with credential issuer to resolve and validate a credential offer presented by the issuer.
• Issuer component: A component that offers all operation required to authorize and submit a credential issuance request.

Resolve Credential Issuer and authorization server metadata

To obtain the credentials issuer metadata use the CredentialIssuerMetadataResolver actor the following way:

import OpenID4VCI

let credentialIdentifier = try CredentialIdentifier(value: "https://....")
let credentialIssuerIdentifier = try CredentialIssuerId(CREDENTIAL_ISSUER_PUBLIC_URL)
    
let resolver = CredentialIssuerMetadataResolver()
let metadata = await resolver.resolve(
    source: .credentialIssuer(
        credentialIssuerIdentifier
    )
)

switch metadata {
    ...
}

In case of failure the reason will be returned in an Error.

To obtain the authorization server's metadata use the AuthorizationServerMetadataResolver the following way:

import OpenID4VCI

let resolver = AuthorizationServerMetadataResolver()
let authServerMetadata = await resolver.resolve(url: "https://....")

The url can be obtained from the credential issuer metadata above.

Resolve a credential offer

A CredentialOfferRequestResolver uses the two metadata resolvers mentioned above internally, to resolve metadata of an issuer and its authorization server

Given a credential offer url use the CredentialOfferRequestResolver the following way to validate and resolve it to a CredentialOffer

import OpenID4VCI

let resolver = CredentialOfferRequestResolver()
let result = await resolver
  .resolve(
    source: try .init(
      urlString: url
    )
  )
    
switch result {
    ...
}

Credential Issuance

The OpenID4VCI specification defines two flows of issuance:

• Authorization Code Flow (wallet-initiated flow)
• Pre-Authorization Code Flow. In this flow, before initiating the flow with the Wallet, the Credential Issuer first conducts the steps required to prepare the Credential issuance.

Issuer

The Issuer is the component that facilitates the authorization and submission of a credential issuance request. It consists of two components:

• IssuanceAuthorizer: A component responsible for all interactions with an authorization server to authorize a request for credential issuance.
• IssuanceRequester: A component responsible for all interactions with a credential issuer for submitting credential issuance requests.

Initialize an Issuer

import OpenID4VCI

let credentialIdentifier = try CredentialIdentifier(value: "https://....")
let credentialIssuerIdentifier = try CredentialIssuerId(CREDENTIAL_ISSUER_PUBLIC_URL)
let offer: CredentialOffer = ...
let config: OpenId4VCIConfig = ...

let issuer = try Issuer(
    authorizationServerMetadata: offer.authorizationServerMetadata,
    issuerMetadata: offer.credentialIssuerMetadata,
    config: config
)

Authorize request via Authorization Code Flow

Given an Issuer use Authorization Code Flow to authorize an issuance request.

import OpenID4VCI

let parPlaced = await issuer.pushAuthorizationCodeRequest(
  credentialOffer: offer
)

if case let .success(request) = parPlaced,
   case let .par(parRequested) = request {
      
    let authorizationCode = ...
    let issuanceAuthorization: IssuanceAuthorization = .authorizationCode(authorizationCode: authorizationCode)
    let unAuthorized = await issuer.handleAuthorizationCode(
        parRequested: request,
        authorizationCode: issuanceAuthorization
      )
      
    switch unAuthorized {
      case .success(let request):
        let authorizedRequest = await issuer.requestAccessToken(authorizationCode: request)
        
        if case let .success(authorized) = authorizedRequest,
           case let .noProofRequired(token) = authorized {
          print("\(token.accessToken)")
        }
        
      case .failure:
        throw ...
      }
    }
    throw ...
}

Authorize request via Pre-Authorization Code Flow

Given an Issuer use Pre-Authorization Code Flow to authorize an issuance request.

import OpenID4VCI

let issuer: Issuer = ...
let preAuthorizationCode = ... // pre-authorization code as contained in a credential offer 
let authorizedRequest = await issuer.authorizeWithPreAuthorizationCode(
    credentialOffer: ...,
    authorizationCode: ...,
    clientId: ...,
    transactionCode: ...
  )

Request a single credential issuance

Given an authorizedRequest and an Issuer a single credential issuance request can be placed as follows

import OpenID4VCI

let payload: IssuanceRequestPayload = .configurationBased(
  credentialConfigurationIdentifier: ...
)

let requestOutcome = try await issuer.request(
    proofRequest: ...,
    bindingKeys: ..., // SigningKeyProxy array
    requestPayload: payload,
    responseEncryptionSpecProvider:  { 
        Issuer.createResponseEncryptionSpec($0) 
    }
)

switch requestOutcome {

}

You can also check the unit tests for more usage examples.

Features supported

Authorization Endpoint

Specification defines (section 5.1.1) that a credential's issuance can be requested using authorization_details parameter when using authorization code flow. Current version of the library does not support that. It only supports requesting issuance using scope parameter in the authorization endpoint.

Token Endpoint

Specification defines (section 6.2) that upon a successful token response authorization_details is included in response, if authorization_details parameter is used in authorization endpoint. Current version of library is not parsing/utilizing this response attribute.

Credential Request

Current version of the library implements integrations with issuer's Crednetial Endpoint and Deferred Crednetial Endpoint endpoints.

NOTE: Attribute credential_identifier of a credential request is not yet supported.

Credential Format Profiles

OpenId4VCI specification defines several extension points to accommodate the differences across Credential formats. The current version of the library fully supports ISO mDL profile and gives some initial support for IETF SD-JWT VC profile.

Proof Types

OpenId4VCI specification (draft 14) defines proofs that can be included in a credential issuance request, JWT proof type in particular. The current version of the library supports JWT proof types.

Notes

Examples for all of the above are located in the test target of the library.

How to contribute

We welcome contributions to this project. To ensure that the process is smooth for everyone involved, follow the guidelines found in CONTRIBUTING.md.

License

Third-party component licenses

• JOSE Support: JOSESwift
• JSON Support: SwiftyJSON

License details

Copyright (c) 2023 European Commission

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.