Fix IndexError in Digest auth header parser on empty values

[mbeijen]

The Digest auth challenge parser called a private unquote helper that index-errored on empty values, so a WWW-Authenticate header like Digest realm=, qop="auth", … would crash instead of being parsed as an empty realm. Switching to value.strip('"') (matching the pattern already used elsewhere for header parsing) fixes that, and also handles unbalanced or repeated quotes — see the rationale in encode/httpx#3771.

Port of encode/httpx#3771 by @JeroenVanZundert, with @akx's .strip('"') improvement applied.

Note: this change was prepared with AI assistance (Claude Code).

[codspeed-hq]

Merging this PR will not alter performance

✅ 15 untouched benchmarks
⏩ 7 skipped benchmarks¹

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_{Comparing mbeijen:fix-unquote-empty-string (d11964a) with main (3146201)}

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}