iRule example to extract specific X509 information: SOL5171

When you say that the $sn variable doesn't have a value, are you saying that because the "Serial" header being inserted is blank? Is the Serial header even being inserted?

I'd add a few logging statements to the rule to be sure things are functioning, or in this case malfunctioning, the way you think they are, and to give us a bit more insight if things are still failing as to what the problem might be.

Something like:

when CLIENTSSL_CLIENTCERT {
  set cert [SSL::cert 0]
  set sn [X509::serial_number $cert]
  log local0. "cert is $cert"
  log local0. "sn is $sn"
}
when HTTP_REQUEST {
  if { [info exists $sn] } {
    HTTP::header insert Serial $sn
    log local0. "sn is $sn"
  }
}

HTH,

Colin