I am trying to implement a third party passkey credential provider and I have been able to successfully setup the project for that. Below is a sample code which I am using -
let passkeyRegistrationCredential = ASPasskeyRegistrationCredential(relyingParty: self.request?.credentialIdentity.serviceIdentifier.identifier ?? "", clientDataHash: self.request?.clientDataHash ?? Data(), credentialID: Data(credentialId), attestationObject: Data(attestationBytes)
self.extensionContext.completeRegistrationRequest(using: passkeyRegistrationCredential)
The attestationBytes object that I am generating and sending back to RP seems to work only if I set the "fmt" to "none", which basically requires "attStmt" to be sent as an empty value as per WebAuthn spec - https://www.w3.org/TR/webauthn-2/#sctn-none-attestation
When trying to set the "fmt" to "packed" in attestation object and creating a self signed "attStmt" consisting of "alg" and "sig" key-values referring - https://www.w3.org/TR/webauthn-2/#sctn-packed-attestation, it does not seem to work. The RP throws an error. I do not have "x5c" object as that supposedly is not mandatory in case of self attestation. I have "authData" also as part of the response properly setup.
Is it not possible to use packed attestation or am I missing something in creating the attestation object? Also, does Apple modify the response being sent in the background before sending to RP if packed fmt is used?