digest: fix OWS and escaped quote handling

[trxvorr]

The migration to the strparse API introduced regressions in Digest authentication parsing where Optional Whitespace (OWS) after commas was not skipped, and escaped quotes in values were not correctly parsed.

This change ensures whitespace is skipped before key lookups and escaped characters are properly handled and unescaped in quoted values.

Reported-by: herdiyanitdev (hackerone)

[trxvorr]

this was the report
https://hackerone.com/reports/3473384

[testclutch]

Analysis of PR #20102 at e3c3ac15:

Test 1664 failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 810 different CI jobs (the link just goes to one of them).

Test 2084 failed, which has NOT been flaky recently, so there could be a real issue in this PR. Note that this test has failed in 296 different CI jobs (the link just goes to one of them). Note that this CI job has had a number of other flaky tests recently (3, to be exact) so it may be that this failure is rather a systemic issue with this job and not with this specific PR.

Test 2500 failed, but it has been 20.1% flaky lately, so it's probably NOT a fault of the PR. Note that this test has failed in 4 different CI jobs (the link just goes to one of them). Note that this CI job has had a number of other flaky tests recently (3, to be exact) so it may be that this failure is rather a systemic issue with this job and not with this specific PR.

Generated by Testclutch

[trxvorr]

@vszakats i think everything is working as intended now could you please check?

[trxvorr]

@vszakats hey hope you're doing well
any updates?

[bagder]

Thanks!