ngx_http_auth_request_module equivance for HAProxy

You can try this Lua-based solution. It's inspired by ngx_http_auth_request_module.

Load the lua script in the global section.

global
    lua-load /usr/share/haproxy/auth-request.lua

Define an auth backend

backend auth_request
    mode http
    server auth_request 127.0.0.1:8080 check

Invoke the Lua check in a frontend and deny the request if it failed.

frontend http
    http-request lua.auth-request auth_request     /is-allowed
    http-request deny if ! { var(txn.auth_response_successful) -m bool }

The author also made a nice blog post, where he explained the inner workings in much detail.

At least for apache (both 1.x and 2.x) you can try out https://github.com/kitech/mod_authnz_external. It runs an external script to handle user's credentials. This script in turn may query an external service over HTTP[s], in this case it would work similarly (not considering performance issues) to ngx_http_auth_request_module