Verifiable Credentials - OpenID Connect Authentication

OpenID Connect Authentication can be used in conjunction with Verifiable Credentials to provide a secure and decentralized way of verifying user identities. Verifiable Credentials are digital credentials that can be issued by trusted authorities and can be presented by users to prove their identity or attributes.

In this role, CAS acts as an OpenID Credential Issuer and extends its existing OpenID Connect capabilities with support for credential issuance, credential metadata publication, proof validation, nonce generation, and wallet-facing issuance flows.

The following capabilities are in place:

  • Issuer metadata is published via the .well-known/openid-credential-issuer endpoint.
  • CAS may issue credentials formats such as SD-JWT VC (selective disclosure), etc.
  • Dedicated endpoints for credential issuance and nonce generation are available.
  • Credential offers may be produced and shared with wallets.
  • Pre-authorized code flows may be used to obtain issuance-scoped access tokens.
  • Access tokens issued for verifiable credential flows may carry authorization context for one or more credential configurations.
  • Proofs may be validated to ensure possession of holder key material and to prevent replay.

Overview

Support is enabled by including the following module in the overlay:



1
2
3
4
5



<dependency>
    <groupId>org.apereo.cas</groupId>
    <artifactId>cas-server-support-oidc-vc</artifactId>
    <version>${cas.version}</version>
</dependency>





1



implementation "org.apereo.cas:cas-server-support-oidc-vc:${project.'cas.version'}"





1
2
3
4
5
6
7
8
9



dependencyManagement {
    imports {
        mavenBom "org.apereo.cas:cas-server-support-bom:${project.'cas.version'}"
    }
}

dependencies {
    implementation "org.apereo.cas:cas-server-support-oidc-vc"
}





1
2
3
4
5
6
7
8
9
10



dependencies {
    /*
        The following platform references should be included automatically and are listed here for reference only.

        implementation enforcedPlatform("org.apereo.cas:cas-server-support-bom:${project.'cas.version'}")
        implementation platform(org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES)
        
    */
    implementation "org.apereo.cas:cas-server-support-oidc-vc"
}

The following settings and properties are available from the CAS configuration catalog:

The configuration settings listed below are tagged as Required in the CAS configuration metadata. This flag indicates that the presence of the setting may be needed to activate or affect the behavior of the CAS feature and generally should be reviewed, possibly owned and adjusted. If the setting is assigned a default value, you do not need to strictly put the setting in your copy of the configuration, but should review it nonetheless to make sure it matches your deployment expectations.

The configuration settings listed below are tagged as Optional in the CAS configuration metadata. This flag indicates that the presence of the setting is not immediately necessary in the end-user CAS configuration, because a default value is assigned or the activation of the feature is not conditionally controlled by the setting value. In other words, you should only include this field in your configuration if you need to modify the default value or if you need to turn on the feature controlled by the setting.

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].claims=

    • Collection of claim definitions supported by this credential configuration. The map key is the logical claim name that will appear in the issued credential, while the value describes how that claim is sourced, typed, and enforced. Claim definitions are typically used to map resolved principal attributes into the final credential payload.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].credential-signing-alg-values-supported=ES256,RS256

    • Lists the signing algorithms supported by the issuer when producing the credential for this configuration. These algorithm identifiers are typically JOSE signature algorithms such as ES256 or RS256, and are advertised in issuer metadata so wallets know what credential signature formats are supported.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].cryptographic-binding-methods-supported=jwk

    • Lists the supported cryptographic binding methods for this credential. These values indicate how the issued credential may be bound to key material controlled by the wallet or holder. A common value is jwk, which indicates binding via a JSON Web Key.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].format=

    • Defines the credential format issued for this configuration. Typical values depend on the verifiable credential profile supported by the issuer, such as JWT-based or SD-JWT-based credentials. This value is published in issuer metadata and is used by wallets to determine how the credential request and response should be processed.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].proof-signing-alg-values-supported=ES256,RS256

    • Lists the signing algorithms supported for proof validation when the wallet submits proof material as part of a credential request. These values represent the algorithms CAS accepts when verifying proof-of-possession tokens or JWT-based proofs presented by the holder.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].scope=

    • OAuth scope associated with this credential configuration. This scope may be used during authorization and token issuance to indicate that the client or wallet is requesting permission to obtain this specific type of verifiable credential.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

  • cas.authn.oidc.vc.issuer.credential-configurations.[key].cryptographic-binding-methods-supported=jwk

    • Lists the supported cryptographic binding methods for this credential. These values indicate how the issued credential may be bound to key material controlled by the wallet or holder. A common value is jwk, which indicates binding via a JSON Web Key.

    org.apereo.cas.configuration.model.support.oidc.OidcVerifiableCredentialConfigurationProperties.

    How can I configure this property?

    This CAS feature is able to accept signing and encryption crypto keys. In most scenarios if keys are not provided, CAS will auto-generate them. The following instructions apply if you wish to manually and beforehand create the signing and encryption keys.

    Note that if you are asked to create a JWK of a certain size for the key, you are to use the following set of commands to generate the token:

    

    1
2

    		

    wget https://raw.githubusercontent.com/apereo/cas/master/etc/jwk-gen.jar
java -jar jwk-gen.jar -t oct -s [size]

    The outcome would be similar to:

    

    1
2
3
4
5

    		

    {
  "kty": "oct",
  "kid": "...",
  "k": "..."
}

    The generated value for k needs to be assigned to the relevant CAS settings. Note that keys generated via the above algorithm are processed by CAS using the Advanced Encryption Standard (AES) algorithm which is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology.

    Configuration Metadata

    The collection of configuration properties listed in this section are automatically generated from the CAS source and components that contain the actual field definitions, types, descriptions, modules, etc. This metadata may not always be 100% accurate, or could be lacking details and sufficient explanations.

    Be Selective

    This section is meant as a guide only. Do NOT copy/paste the entire collection of settings into your CAS configuration; rather pick only the properties that you need. Do NOT enable settings unless you are certain of their purpose and do NOT copy settings into your configuration only to keep them as reference. All these ideas lead to upgrade headaches, maintenance nightmares and premature aging.

    YAGNI

    Note that for nearly ALL use cases, declaring and configuring properties listed here is sufficient. You should NOT have to explicitly massage a CAS XML/Java/etc configuration file to design an authentication handler, create attribute release policies, etc. CAS at runtime will auto-configure all required changes for you. If you are unsure about the meaning of a given CAS setting, do NOT turn it on without hesitation. Review the codebase or better yet, ask questions to clarify the intended behavior.

    Naming Convention

    Property names can be specified in very relaxed terms. For instance cas.someProperty, cas.some-property, cas.some_property are all valid names. While all forms are accepted by CAS, there are certain components (in CAS and other frameworks used) whose activation at runtime is conditional on a property value, where this property is required to have been specified in CAS configuration using kebab case. This is both true for properties that are owned by CAS as well as those that might be presented to the system via an external library or framework such as Spring Boot, etc.

    :information_source: Note

    When possible, properties should be stored in lower-case kebab format, such as cas.property-name=value. The only possible exception to this rule is when naming actuator endpoints; The name of the actuator endpoints (i.e. ssoSessions) MUST remain in camelCase mode.

    Settings and properties that are controlled by the CAS platform directly always begin with the prefix cas. All other settings are controlled and provided to CAS via other underlying frameworks and may have their own schemas and syntax. BE CAREFUL with the distinction. Unrecognized properties are rejected by CAS and/or frameworks upon which CAS depends. This means if you somehow misspell a property definition or fail to adhere to the dot-notation syntax and such, your setting is entirely refused by CAS and likely the feature it controls will never be activated in the way you intend.

    Validation

    Configuration properties are automatically validated on CAS startup to report issues with configuration binding, especially if defined CAS settings cannot be recognized or validated by the configuration schema. Additional validation processes are also handled via Configuration Metadata and property migrations applied automatically on startup by Spring Boot and family.

    Indexed Settings

    CAS settings able to accept multiple values are typically documented with an index, such as cas.some.setting[0]=value. The index [0] is meant to be incremented by the adopter to allow for distinct multiple configuration blocks.

    Endpoints

    The following endpoints are typically involved in the verifiable credential issuance flow.

    Issuer Metadata

    Publishes issuer capabilities and supported credential configuration metadata.

    

    1

    		

    GET /oidc/.well-known/openid-credential-issuer

    This endpoint generally advertises:

    • The credential issuer identifier.
    • The credential endpoint.
    • The nonce endpoint, when supported.
    • Supported credential configurations.
    • Supported formats and signing algorithms.

    • Credential Endpoint

    Issues a verifiable credential to the wallet once the access token, proof, and requested credential configuration have been validated.

    

    1

    		

    POST /oidc/oidcVcCredential

    This endpoint expects:

    • A bearer access token.
    • A requested credential_configuration_id.
    • A proof object with a nonce as a claim.

    The endpoint body is expected as:

    

    1
2
3
4
5
6
7

    		

    {
  credential_configuration_id: "myorg",
  proof: {
    proof_type: "jwt",
    jwt: proof
  }
}

    Nonce Endpoint

    Produces a fresh c_nonce that may be used by the wallet in a later proof for the credential request.

    

    1

    		

    POST /oidc/oidcVcNonce

    This endpoint typically returns:

    • c_nonce
    • c_nonce_expires_at

    Credential Offer Endpoint

    Exposes a prepared credential offer for a previously-created issuance transaction.

    

    1

    		

    GET /oidc/oidcVcCredentialOffer/{transactionId}

    This endpoint does not establish subject identity on its own. Instead, it dereferences a short-lived server-side issuance transaction and returns the corresponding credential offer document.

    Trusted Transaction Creation Endpoint

    Creates a server-side issuance transaction for a known subject and returns an opaque transaction identifier and a wallet-facing offer URI.

    

    1

    		

    POST /oidc/oidcVcCredentialOfferTransactions

    The endpoint body is expected to be:

    

    1
2
3
4

    		

    {
  "principal": "...",
  "credentialConfigurationIds": ["..."]
}

    This endpoint is intended for trusted callers such as:

    • Administrative tools
    • Internal backend services & APIs
    • Authenticated CAS user interfaces

    This endpoint is protected and should not be exposed as an anonymous wallet-facing API.

    Token Endpoint

    Exchanges an authorization artifact, such as a pre-authorized code, for an access token that may later be used at the credential endpoint.

    

    1

    		

    POST /oidc/token

    When used for verifiable credential issuance, this endpoint may:

    • Accept the pre-authorized_code grant.
    • Require a tx_code.
    • Return a c_nonce.
    • Produce an access token that is scoped to credential issuance.

    Example request:

    

    1
2
3
4
5
6

    		

    POST /oidc/token
Content-Type: application/x-www-form-urlencoded

grant_type=urn:ietf:params:oauth:grant-type:pre-authorized_code&
pre-authorized_code=L0Qw0sT6dP5P7l7xM0H2AqQ0g9vM2j5fByuYwQ&
tx_code=TST-1234

    Nonce Proof

    Proofs are expected to carry a nonce claim. The nonce lets CAS tell whether the wallet’s proof is fresh, instead of a replay. In OIDC4VCI, the wallet sends a proof showing it controls the key the credential should be bound to, and the c_nonce is the primary defense against replay of that proof.

    Without a nonce, an attacker who somehow gets hold of a previously valid proof could try to send it again and get a duplicate credential issued to the same key.

    In practical terms, the flow is:

    • The wallet asks CAS for a fresh c_nonce from the nonce endpoint, or receives one from the token endpoint.
    • The wallet builds its proof and includes that nonce.
    • CAS checks that the nonce matches one it issued, is still fresh, and has not already been used.
    • CAS consumes it so the same proof cannot be replayed.

    The token endpoint issues the nonce. The credential endpoint enforces it while validating the proof.

    Pre-Authorized Code Flow

    In pre-authorized code flows, CAS or a trusted backend prepares the issuance transaction before the wallet starts the OAuth exchange.

    The general flow is:

    • A trusted caller creates an issuance transaction.
    • CAS stores the transaction and issues a pre-authorized code.
    • CAS returns a wallet-facing credential_offer_uri.
    • The wallet resolves the offer.
    • The wallet exchanges the pre-authorized code at the token endpoint.
    • CAS returns an access token, and optionally a c_nonce.
    • The wallet calls the credential endpoint with the access token and proof.
    • CAS validates the request and issues the credential.

    Credential Signing

    After claims are collected and validated, CAS signs the credential using issuer key material.

    For JWT-based credential formats, this generally reuses the same signing infrastructure used for ID tokens and other JWT artifacts, while still producing a payload that is specific to the verifiable credential format being issued.