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.

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.

Overview

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



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





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





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

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





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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.nonce-ttl=PT60S

    • Control how long a nonce should last.

    This settings supports the java.time.Duration syntax [?].

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

    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:

    

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    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:

    

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    {
  "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.

    Flow

    The flow starts with CAS publishing issuer metadata at /.well-known/openid-credential-issuer. This document advertises the issuer identifier, the credential endpoint, supported credential configurations, and, when implemented, the nonce endpoint. Wallets use this metadata to discover what CAS can issue and how to interact with it.

    Before requesting a credential, the wallet obtains authorization using OAuth 2.0 mechanisms associated with the credential issuer or its authorization server. OIDC4VCI is explicitly built on OAuth 2.0, and the wallet uses OAuth authorization to gain the right to receive one or more credentials from the issuer.

    Once the wallet has an access token, CAS uses its existing access token and principal resolution machinery to identify the authenticated subject. At this point, CAS has the Principal and its attributes, which become the source data for the credential claims that may be issued.

    CAS then selects the requested credential_configuration_id from issuer metadata and maps principal attributes into credential claims according to that configuration. In practice, this is typically configuration-driven, so each claim definition identifies its source principal attribute, whether it is mandatory, and how it should be typed or normalized before issuance.

    When credential binding is required, the wallet sends a proof with the credential request to demonstrate possession of the key material to which the credential should be bound. OIDC4VCI supports proof-based issuance so that the issued credential can be tied to wallet-controlled cryptographic material rather than being just a bearer artifact.

    The wallet calls the credential endpoint with its access token, the requested credential configuration, and, if required, the proof. CAS validates the access token, validates the proof, checks the requested credential configuration, resolves claims from the principal, and prepares the credential payload for issuance.

    After claims are prepared, CAS signs the credential using its issuer key material. For JWT-based credential formats, this can reuse the same underlying JWS signing infrastructure CAS already uses for ID tokens, although the credential payload is distinct from an ID token and follows verifiable credential format rules instead.

    Nonce Proof

    Proofs are expected to carry a nonce claims. 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 spec says c_nonce is the main 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:

    • Wallet asks CAS for a fresh c_nonce from the nonce endpoint.
    • 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.