HAProxy: Deny a request while keeping the client-connection alive

haproxy.cfg

frontend main
  bind :443 ssl crt /tmp/foo.pem
  
  mode http
  option http-keep-alive
  
  # ...
  
  use_backend bk_deny if { path_beg /you/didnt/say/the/magic/word }
  
  default_backend bk_servers
  
frontent deny
  bind 127.0.0.1:8001
  mode http
  
  http-request deny
 
backend bk_servers
  # your normal servers
  server foo 10.42.42.42:80
  server bar 10.23.23.23:80
  
backend bk_deny
  server deny 127.0.0.1:8001