HAPROXY: Use a fetched integer value as checked value in an ACL

haproxy.cnf

# First extract the rate into a variable called req.src_http_req_rate
http-request content set-var req.src_http_req_rate %[src_http_req_rate]

# Then use this variable in the acl by subtracting the current rate from the
# value returned from the map. If the result is less than 0, the request rate
# is larger than the allowed value
acl abuse src,map_ip_int(/etc/haproxy/ips.map),sub(req.src_http_req_rate) -m int lt 0