[mod_auth] refactor out auth backend code
[mod_auth] refactor out auth backend code

separate subroutines in http_auth.c

PatchyFog/lighttpd1.4-mbedtls,PatchyFog/lighttpd1.4-mbedtls,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,PatchyFog/lighttpd1.4-mbedtls,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,PatchyFog/lighttpd1.4-mbedtls