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Delegation of Authentication Extension (delegation)

This extension allows one Client to create a token that can be used by a third-party (here called the Delegate) to gain authenticate to the Relying Party. The Delegate is a WebAuthn Client that may be either owned by the same user or may be owned by another trusted party. This allows behavior similar to "password-sharing" for WebAuthn without proceeding through the Registration Flow once for each Relying Party and Client pair. The Client can also place contraints on the Delegate using this extension. The new flexibility also allows for recovery flows that are more efficient.

Extension identifier

delegation

Operation applicability

Registration

Client extension input

The Boolean value true to indicate that this extension is supported by the Relying Party.

partial dictionary AuthenticationExtensionsClientInputs {
  boolean delegation;
};

Client extension processing

If the client wishes to produce a delegatable credential, perform the following steps:

  1. Let delegation be a DelegationExtensionOutputs with action = "create"
  2. Let delegation.use = null
  3. Let delegation.create be a non-null DelegationCreationOptions.
    1. Let delegation.create.options.user be the PublicKeyCredentialUserEntity from the Relying Party's PublicKeyCredentialCreationOptions
    2. Let delegation.create.options.expiration reflect how long to allow the credential to work. A null value signifies no expiration policy.
    3. Let delegation.create.options.uses reflect how many times the credential should work. A null value signifies no limit in uses.
    4. Let delegation.create.options.allowCredentials reflect any pubkeys that are allowed. If null, then all credentials are allowed.
    5. Let delegation.create.serializedOptions be a JSON serialization of delegation.create.options.
  4. Let secret be a random byte array. The secret MAY be generated from a cryptographically secure random number generator. The secret also MAY be generated as the output of a Key Derivation Function.
  5. Let delegation.create.challenge be SHA-256-HMAC(delegation.create.serializedOptions, secret)
  6. Store or transfer secret in a trusted manner. The encoding and means of communication are not specified by this document.
  7. Return delegation.

If the client wishes to use a delegatable credential, perform the following steps:

  1. Let delegation be a DelegationExtensionOutputs with action = "use".
  2. Let delegation.create = null.
  3. Obtain the secret used when processing this extension at registration, and store it in delegation.use.response. If this fails, return an error.
  4. Return delegation.

If the client wishes to do neither, the client should not process this extension. If it is being processed, then return an "AbortError" DOMException.

Client extension output

enum DelegationIdentifier { "create", "use" };

dictionary DelegationCreationOptions {
    PublicKeyCredentialUserEntity user;
    unsigned long long? expiration = null;	
    unsigned long? uses = 1;
    sequence<PublicKeyCredentialDescriptor>? allowCredentials = [];
}

dictionary DelegationCreation {
    BufferSource challenge;
    DelegationCreationOptions options;
    ArrayBuffer serializedOptions;
}

dictionary DelegationUse {
    BufferSource response;
}

dictionary DelegationExtensionOutputs {
    DelegationIdentifier action;
    DelegationCreationOptions? create;
    DelegationUse? use;
}

partial dictionary AuthenticationExtensionsClientOutputs {
    DelegationExtensionOutputs delegation;
};

Relying Party extension validation

All failed verifications MUST return an error.

If delegation.action = "create":

  1. Verify delegation.create is non-null.
  2. Verify delegation.create.serializedOptions when deserialized is equivalent to delegation.create.options.
  3. Verify that the delegation.create.options.user value is equal to the user field in the sent PublicKeyCredentialCreationOptions.
  4. If the authentication suceeds, the Relying Party SHOULD store delegation.create until expiration milliseconds after the UNIX epoch and with associated data of the number of uses. The Relying Party MUST NOT store delegation.create if authentication fails.
  5. Return success.

If delegation.action = "use":

  1. Verify delegation.use is non-null
  2. For all DelegationCreation objects associated with the current connection's user handle, create (on failed verification continue the loop):
    1. Verify that create.expiration is less than the number of milliseconds since the UNIX epoch.
    2. Verify that the associate use counter with this DelegationCreation is not equal to or greater than the number of allowed uses.
    3. If create.allowCredentials is not null, then verify that the public key of the Delegate's authenticatorData is in the sequence.
    4. Verify that SHA-256-HMAC(create.serializedOptions, create.challenge) = delegation.use.response
    5. Increment the number of uses for this DelegationCreation.
    6. Return success.
  3. Return an error.

If this extension is processed successfully and the registration flow succeeds, then the Relying Party should associate the public key used for registration with the user handle that generated the challenge.

Authenticator extension input

None.

Authenticator extension processing

None.

Authenticator extension output

None.