Access by reverse dns lookup

I know this is over a decade too late - but I've recently had the issue of having a support company with a dynamic DNS record wanting to be able to access the login URL of our website.  We have a list of static IPs in IPS_OF_MANAGEMENT_HOSTS - but they wanted to add their DYNAMIC.DNS.NAME entry as well.

It may not be pretty - but here's what I did, hopefully it'll help someone (note that I put the calculation as far into the process as possible to minimise the chance of it running):

when HTTP_REQUEST {
	switch -glob [string tolower [HTTP::host]] {  
        "example.com" {
		    switch -glob [string tolower [HTTP::uri]] {
				"/logonpage*" {
					if { [class match [IP::client_addr] equals IPS_OF_MANAGEMENT_HOSTS] } {
						pool BACKEND_SERVERS
					} else {
                        set IPlookup [RESOLVER::summarize [RESOLVER::name_lookup "/Common/rr" DYNAMIC.DNS.NAME a] ]
                        set match "0"
                        foreach result $IPlookup {
                            if { [IP::client_addr] equals [lindex $result 4] } {
                                set match "1"
                                }
                            }
                        if {$match == 1} {
                            pool BACKEND_SERVERS
                        } else {
						    HTTP::respond 403 content "Access denied"
						    return
                            }
						}
					}
				default {
					pool BACKEND_SERVERS
					}
				}
			}
		}
	}

 Note that you will've had to define your resolvers in TMSH in order to refer to it here.  In theory it'll work where DNS returns multiple entries - although I haven't tested it.