Comment 4 for bug 1918439

https://www.haproxy.com/blog/four-examples-of-haproxy-rate-limiting/:

"""
* Sliding Window Rate Limiting

frontend website
    bind :80
    stick-table type ipv6 size 100k expire 30s store http_req_rate(10s)
    http-request track-sc0 src
    http-request deny deny_status 429 if { sc_http_req_rate(0) gt 20 }
    default_backend servers
"""