auth rest-api: fix signedness bug in json data normalization

[miodvallat]

Short description

As reported a few minutes ago, escaped characters (\nnn) in Json input were not normalized correctly.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Coverage Report for CI Build 31101790837

Coverage increased (+5.6%) to 71.169%

Details

• Coverage increased (+5.6%) from the base build.
• Patch coverage: 1 of 1 lines across 1 file are fully covered (100%).
• 14 coverage regressions across 4 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

14 previously-covered lines in 4 files lost coverage.

File	Lines Losing Coverage	Coverage
pdns/recursordist/test-syncres_cc1.cc	6	80.16%
pdns/recursordist/pdns_recursor.cc	3	75.69%
pdns/recursordist/recpacketcache.hh	3	91.14%
pdns/recursordist/aggressive_nsec.cc	2	65.96%

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Coverage Stats

Relevant Lines:	173008
Covered Lines:	135007
Line Coverage:	78.04%
Relevant Branches:	82766
Covered Branches:	47026
Branch Coverage:	56.82%
Branches in Coverage %:	Yes
Coverage Strength:	6886861.68 hits per line

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💛 - Coveralls