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Issuance

UniCore can be used for creating and issuing Verifiable Credentials based on defined configurations and client requests. This process involves validating input data, applying the correct credential formats and types, and signing or encoding the credentials for issuance. The errors documented in this section relate to possible failure scenarios encountered during credential issuance, such as misconfigured credential configurations, invalid data in the credential subject, or missing required elements.

Invalid Credential Type​

This error is raised when the credential provided in the request does not match the expected type based on its signed status. Specifically:

  • Signed Credentials: The credential must be provided as a string representing a verifiable credential signed as a JWT.
  • Unsigned Credentials: The credential must be provided as a JSON object.

If the credential's type does not meet these requirements, the API returns a 400 Bad Request error.

Resolution​

  • For signed credentials, ensure that the credential value is a valid JWT containing a properly signed verifiable credential.
  • For unsigned credentials, verify that the credential value is a well-formed JSON object with all the necessary fields for credential issuance.

Review your request payload to confirm that the credential type aligns with these expectations.

No Credential Configuration Found​

This error is raised when the system cannot find a credential configuration that matches the provided credentialConfigurationId. This indicates that either the specified configuration does not exist or it has not been properly set up in the server's settings.

Resolution​

  • Verify the Identifier:
    Ensure that the credentialConfigurationId in your request is correct.

  • Review Server Configuration:
    Verify that the desired credential configuration is defined in the credential_configurations section of your config.yaml file. Ensure that the credentialConfigurationId provided in your request exactly matches the credential_configuration_id of the intended configuration.

Unsupported Credential Format​

This error is raised when UniCore encounters a credential configuration that specifies a format it cannot process. This typically occurs when the credential configuration’s format does not match any of the supported formats.

Resolution​

Currently UniCore only supports the jwt_vc_json format. This configuration needs to be set through the credential_configurations property in the config.yaml file, e.g.:

credential_configurations:
  - credential_configuration_id: my-credential-configuration-id
    format: jwt_vc_json
    credential_definition:
      type:
        - VerifiableCredential

Unsupported Credential Type​

This error is raised when UniCore encounters a credential type that is not recognized or supported by the current implementation. In practice, it means that none of the credential types provided in the configuration match any of the types UniCore is configured to process. For example, supported types might include VerifiableCredential, AchievementCredential, or OpenBadgeCredential.

Resolution​

UniCore supports three primary credential models:

For all models, the credential type must be declared in the credential_definition property of your credential configuration (in the config.yaml file). Ensure that the configuration includes the base type VerifiableCredential along with any additional types required by your credential model.

For example:

For W3C Verifiable Credentials:

credential_configurations:
  - credential_configuration_id: my-w3c-vc-configuration-id
    format: jwt_vc_json
    credential_definition:
      type:
        - VerifiableCredential

For OpenBadgeV3 Credentials:

credential_configurations:
  - credential_configuration_id: my-obv3-configuration-id
    format: jwt_vc_json
    credential_definition:
      type:
        - VerifiableCredential
        - OpenBadgeCredential

For Custom W3C Verifiable Credentials:

credential_configurations:
  - credential_configuration_id: my-custom-w3c-vc-configuration-id
    format: jwt_vc_json
    credential_definition:
      type:
        - VerifiableCredential
        - MyCustomCredential

Invalid Credential Subject​

This error occurs when the credentialSubject provided during credential creation does not adhere to the expected format or schema. In other words, the data representing the credential's subject is either malformed, missing required properties, or contains values that fail to meet the validation criteria for the specified credential type.

Resolution​

While the credentialSubject is generally a JSON object that can contain arbitrary data, specific credential types may impose stricter requirements on its structure and content. For example, OpenBadgeV3 credentials require a more defined schema (see OpenBadgeV3 Achievement Credential Specification).

To resolve this error, ensure that the credentialSubject conforms exactly to the expected structure as defined in the credential configuration corresponding to the submitted credentialConfigurationId.

Invalid Identifier Error​

This error indicates that the identifier provided in the credential data is invalid. It is raised when the id field is missing or its value cannot be parsed as a valid URI.

Resolution​

Ensure that the id field is a properly formatted string representing a valid URI. Note that the requirement for an id field varies by credential type: for W3C Verifiable Credentials the id is optional, while for OpenBadgeV3 credentials it is required.

Examples of valid id values:

{
  "id": "https://example.com/credentials/123",
  "credentialSubject": {
    ...
  }
}
{
  "id": "uurn:uuid:6e8bc430-9c3a-11d9-9669-0800200c9a66",
  "credentialSubject": {
    ...
  }
}

Invalid Expiration Date​

This error occurs when the expiresAt value provided for the credential is invalid. It is typically triggered when the expiration date exceeds the maximum allowed value (9999-12-31T23:59:59Z) or when it does not conform to the expected date-time format.

Resolution​

Ensure that the expiresAt value is a valid date-time string and falls within the acceptable range (up to 9999-12-31T23:59:59Z). If the credential should not expire, you may also set expiresAt to "never", although providing an explicit expiration date is generally recommended.

info

The expiresAt field accepts either a valid date-time string or the special value "never" to indicate that the credential does not expire.

Missing Credential Offer​

This error occurs when UniCore cannot locate a Credential Offer for the provided offerId. It typically indicates that an operation is being attempted on a Credential Offer that has not been created or is otherwise unavailable.

Resolution​

Verify that a Credential Offer with the specified offerId exists before proceeding. If the Credential Offer is missing, create it using the POST /v0/offers endpoint.

Send Credential Offer Error​

This error is raised when UniCore fails to send the Credential Offer to the specified target URL. It is triggered when the HTTP request does not complete successfully.

Resolution​

Check the target URL and ensure that it is reachable and correctly configured to receive the Credential Offer.