response header for DNT (tracking-status-values)

tkheader.php

/*
* @info https://www.w3.org/TR/tracking-dnt/#tracking-status-value

*/
function getRequestTrackingStatusValue(){

  return "N";

/*
TSV    = %x21   ; "!" — under construction
       / %x3F   ; "?" — dynamic
       / %x47   ; "G" — gateway to multiple parties
       / %x4E   ; "N" — not tracking
       / %x54   ; "T" — tracking
       / %x43   ; "C" — tracking with consent
       / %x50   ; "P" — tracking only if consented
       / %x44   ; "D" — disregarding DNT
       / %x55   ; "U" — updated
  */       
}
if(isset($_SERVER['HTTP_DNT']) && $_SERVER['HTTP_DNT'] == 1){
  
  header("Tk: " . getRequestTrackingStatusValue());
  
} else {

}