[Fix]: Fixed an header parsing issue concerning authentication

[douxxtech]

This PR fixes #32. The issue was it parsing for Authorization instead of authorization (after header lowercasing by LOWERCASE_HEADERS).

[github-actions]

START + GET /: 165 syscalls
Fastest: 0.000013s (arch_prctl)
Slowest: 0.885390s (accept)

threads: 4 (auto), conns: 50, duration: 20s

[wrk]
Running 20s test @ http://127.0.0.1:8080/
  4 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     3.76ms   10.25ms 422.13ms   99.44%
    Req/Sec     2.35k   568.03     3.85k    72.12%
  187260 requests in 20.03s, 284.13MB read
  Socket errors: connect 0, read 2369, write 0, timeout 0
Requests/sec:   9348.23
Transfer/sec:     14.18MB