Production-Grade Implementation Guidance: DCError Matrices, Retry Strategies, and Simulator Testing for App Attest APIs

Hi there,

We're implementing Apple's DeviceCheck App Attest for production iOS authentication. The public documentation defines DCError cases but doesn't specify which errors are expected per API method or recommend retry/remediation strategies. We need Apple's guidance to implement robust, production-aligned error handling before rollout.

1. Error Surface per API Method

Question: Can you confirm the complete, officially expected set of DCError values for each method?

We understand the following errors are possible across App Attest APIs:

• invalidKey
• invalidInput
• featureUnsupported
• serverUnavailable
• unknownSystemFailure

Specifically, please confirm which errors can occur for:

• DCAppAttestService.generateKey()
• DCAppAttestService.attestKey(_:clientData:)
• DCAppAttestService.generateAssertion(keyID:clientData:)

Are there any additional undocumented or edge-case errors we should handle?

2. Retry Strategy & Remediation Matrix

Question: For each API method and error code, please help us with proposal around which errorCode is retriable, whats the remediation pre retry, retry cap and backoff strategy:

Kindly also help with errors that are not covered here:

Specific sub-questions:

1. invalidKey handling: When this error occurs:

   • Should the app delete the key and call generateKey again?
   • Or should it fail the entire flow?

2. serverUnavailable handling:

   • Should we retry immediately, or wait before retrying?
   • Is exponential backoff recommended?
   • What's the recommended max retry count?

3. Backoff strategy:

   • Which errors (if any) qualify for exponential backoff?
   • Recommended base delay, max delay, and jitter approach?
   • When should we give up and fail the request?

4. unknownSystemFailure:

   • Is this retriable or should we fail?
   • Any known causes or mitigations?

3. Simulator Testing

Questions:

1. Simulator API behavior:
   • Can App Attest APIs be called normally on iOS Simulator? If not, is there a way to simulate for testing.
   • Do they complete successfully with simulated attestations, or do they fail?

Thanks, Nirekshitha