When you get the ASAuthorizationPlatformPublicKeyCredentialAssertion back you can parse it to get the necessary data like credentialID. Since Swift uses regular base64 strings you will have to convert them to base64URL strings then add them to a httpBody and send it to your server for assertion case let credentialAssertion as ASAuthorizationPlatformPublicKeyCredentialAssertion:             print("A credential was used to authenticate: \(credentialAssertion)")             // Verify the below signature and clientDataJSON with your service for the given userID.             let signature = credentialAssertion.signature             let clientDataJSON = credentialAssertion.rawClientDataJSON             let authenticatorData = credentialAssertion.rawAuthenticatorData let credentialID = credentialAssertion.credentialID