Error struct returned by all HTTPDigest functions.
The reason atoms are a stable, SemVer-guarded contract:
:malformed_header- Structured Fields parse failure, or a dictionary value of the wrong type for the field:digest_mismatch- computed digest differs (carriesalgorithm):no_supported_algorithm- header parsed, but no member intersects the:supportedlist:insecure_algorithm_refused- only deprecated algorithms matched andallow_insecure: truewas not set (carriesalgorithm):empty_header- header present but the dictionary is empty:unknown_algorithm-on_unknown: :errorand an unregistered key was present (carriesalgorithmas a string):invalid_preference- Want-* preference outside 0..10