[PR #1051/6c6a5c22 backport][0.28] Refactor the auth mechanism selection algorithm

[patchback[bot]]

This is a backport of PR #1051 as merged into main (6c6a5c2243da605459aaf0ddfc97f3a882ad0f7f).

This fixes some regressions for wrongly identified auth mechanisms when parsing the security_schemes from the openapi document. Also the whole selection decision tree is mapped onto a better function call dependency chain.