Refactor authorization status polling #44
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Pull Request Overview
This PR refactors the authorization status polling mechanism to improve reliability and reduce unnecessary retry attempts. The changes replace fixed retry counts with configurable timeouts and implement exponential backoff strategies.
Key changes:
- Replaces fixed retry counters with configurable timeout-based retry policies
- Implements exponential backoff with maximum interval limits for better server behavior
- Consolidates challenge handling logic by removing the separate
do_challengemethod
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Previously, we assumed that we should poll the challenge URL until completion, because all the servers we tested correctly responded to a POST-as-GET to the challenger URL. We also made an initial POST-as-GET request to fetch the status and skip the challenges in "valid" state. RFC8555 7.5.1 specifies that we should poll the authorization resource status instead. Additionally, the discussion around Errata ID 6317 implies that it is harmful to initiate multiple challenges, as a single failure invalidates the whole authorization. Given the above, we can simplify the code and proceed to poll the authorization status after initiating the first available challenge.
Previously, we limited polling for challenge and order status to a fixed number of tries. The updated algorithm will use increasing intervals and give up when the total wait timeout has elapsed.
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Looks good with one remark:
request retrying logic may be made more complicated then simple repetition with fixed interval and fixed overall times. It gives fast failure in case of permanent network errors but may lead to unnecessary failures if error conditions are temporary. But this may be postponed to adding fatal error checking in future.
Tested with:
Fixes: #29
Fixes: #37
Fixes: #40