Does an equivalent module to nginx's
ngx_http_auth_request_module exist for HAProxy or Apache? This module allows support for custom authentication through HTTP. I quote:
ngx_http_auth_request_modulemodule (1.5.4+) implements client authorization based on the result of a subrequest. If the subrequest returns a 2xx response code, the access is allowed. If it returns 401 or 403, the access is denied with the corresponding error code. Any other response code returned by the subrequest is considered an error.