Factor out Http auth parse logic, test it. #11773

Job	Run time
build_js	2m 9s
build_js	2m 9s
build_details	2s
build_details	2s
build_opam (4.14.x)	8m 52s
build_opam (4.14.x)	8m 52s
build_opam (5.2.x)	5m 44s
build_opam (5.2.x)	5m 44s
build_no_depopts	6m 11s
build_no_depopts	6m 11s
lezer_parse	50s
lezer_parse	50s
build_win32 (x64)	17m 48s
build_win32 (x64)	17m 48s
build_posix (debian_trixie, amd64)	15m 27s
build_posix (debian_trixie, amd64)	15m 27s
run_tests (@citest)	12m 48s
run_tests (@citest)	13m 27s
build_posix (debian_bookworm, amd64)	14m 56s
build_posix (debian_bookworm, amd64)	14m 56s
tree_sitter_parse	51s
tree_sitter_parse	51s
run_tests (@doctest)	8m 11s
run_tests (@doctest)	8m 11s
update_doc	0s
update_doc	0s
build_posix (ubuntu_oracular, amd64)	14m 59s
build_posix (ubuntu_oracular, amd64)	14m 59s
run_tests (@mediatest)	12m 44s
run_tests (@mediatest)	12m 44s
build_posix (ubuntu_noble, amd64)	14m 26s
build_posix (ubuntu_noble, amd64)	14m 26s
build_posix (alpine, amd64)	13m 6s
build_posix (alpine, amd64)	13m 6s
fetch_s3_artifacts	19s
fetch_s3_artifacts	19s
build_docker (amd64)	2m 16s
build_docker (amd64)	2m 16s
build_docker_minimal	0s
build_docker_alpine	0s
build_docker_alpine_minimal	0s
build_docker_release-minimal	0s
build_docker_release-minimal	0s
update_release	0s
update_release	0s
build_docker_release	0s
build_docker_release	0s
build_docker_alpine (amd64)	1m 24s
build_docker_minimal (amd64)	2m 17s
build_docker_alpine_minimal (amd64)	49s
	5h 8m 27s

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