Uses F5 LTM iRule to set referrer policy header for given array of domains

Site-ReferrerHeader.irule

#Referrer-Policy iRule
#By: Pierce Fortin ([email protected])
#Checks for domain being requested on HTTP_Request, Sets flag for response rewrite if match 
#If match, It then checks for Referrer-Policy as existing, if it doesn't exist it adds one
#If match and header !exist, It adds it.
#v1.0 6/19/2018 Initial write


when RULE_INIT 
{
	set static::referrerDebugOn 0
}
when CLIENT_ACCEPTED 
{
	set logPrefix "[IP::client_addr]:[TCP::client_port]:referrer:\[HTTPS\]:\t"
	if { $static::referrerDebugOn } { log local0. "$logPrefix: Client accepted" }
}

when HTTP_REQUEST {
	if { $static::referrerDebugOn } { log local0. "$logPrefix: ### Begin processing Incoming" }
	set isreferrerDomain 0
    array set referrerDomains 
    {
        "domain.com" 
        "domain2.com"
    }
    foreach domain [array get referrerDomains]
    {
		if { $static::referrerDebugOn } { log local0. "$logPrefix: Checking [HTTP::host] against $domain" }
        if { [string tolower [HTTP::host]] eq [string tolower $domain] } {
			if { $static::referrerDebugOn } { log local0. "$logPrefix: Current request is an referrer domain. Processing" }
        	set isreferrerDomain 1
   		}
	}
}

when HTTP_RESPONSE {
	if { $static::referrerDebugOn } { log local0. "$logPrefix: Processing Response" }
    if { $isreferrerDomain eq 1 } {
    	if { $static::referrerDebugOn } { log local0. "$logPrefix: Current request is an referrer domain. Inserting referrer" }
        if { not([HTTP::header exists "Referrer-Policy"])}{
            if { $static::referrerDebugOn } { log local0. "$logPrefix: Could not find existing Referrer-Policy header. Inserting" }
            HTTP::header insert "Referrer-Policy" "no-referrer-when-downgrade"
        }
        else {
            if { $static::referrerDebugOn } { log local0. "$logPrefix: Found existing Referrer-Policy header, Replacing" }
            HTTP::header replace "Referrer-Policy" "no-referrer-when-downgrade"
        }     
	}
}