Specify Multiple Subdomains with Access Control Origin

Question

I am trying to allow access to every subdomain on my site in order to allow cross subdomain AJAX calls. Is there a way to specify all subdomains of a site like *.example.c

Answer 1

Here's how I did it.

The Origin header is specified by the browser and will contain the domain that requested the script on the other domain:

Origin: http://www.websiteA.com

Therefore you can "whitelist" multiple domains in your server-side script:

$allowedOrigins = [
    "http://www.websiteA.com",
    "https://www.websiteB.com"
    // ... etc
];

What you can then do is check if the $_SERVER["HTTP_ORIGIN"] global contains a domain within that whitelist:

if (in_array($_SERVER["HTTP_ORIGIN"], $allowedOrigins)) {

And set the Access-Control-Allow-Origin response header to whatever Origin header value was:

header("Access-Control-Allow-Origin: " . $_SERVER["HTTP_ORIGIN"]);

Full script:

$allowedOrigins = [
    "http://www.websiteA.com",
    "https://www.websiteB.com"
    // ... etc
];

if (in_array($_SERVER["HTTP_ORIGIN"], $allowedOrigins)) {
    header("Access-Control-Allow-Origin: " . $_SERVER["HTTP_ORIGIN"]);
}

Answer 2

//Function to be called first in php file.
function CORS_HEADERS_HANDLER(){
  if (isset($_SERVER['HTTP_ORIGIN'])){
    switch($_SERVER['HTTP_ORIGIN']){
        //Handle an IP address and Port
      case 'http://1.2.3.4:4200':
        header('Access-Control-Allow-Origin: http://1.2.3.4:4200');
        break;
        //Handle an Website Domain (using https)
      case 'https://www.someSite.com':
        header('Access-Control-Allow-Origin: https://www.someSite.com');
        break;
        //Handle an Website Domain (using http)
      case 'http://www.someSite.com':
        header('Access-Control-Allow-Origin: http://www.someSite.com');
        break;
        //Catch if someone's site is actually the reject being cheeky
      case 'https://not.you':
        header('Access-Control-Allow-Origin: https://nice.try');
        break;
        //Handle a rejection passing something that is not the request origin.
      default:
        header('Access-Control-Allow-Origin: https://not.you');
        break;
    }
  }else{
    header('Access-Control-Allow-Origin: https://not.you');
  }
  header('Access-Control-Allow-Methods: GET, POST, PATCH, PUT, DELETE, OPTIONS');
  header('Access-Control-Allow-Headers: Origin, Content-Type, X-Auth-Token');
  header('Access-Control-Allow-Credentials: true');
  header('Content-Type: application/json; charset=utf-8');
  header("Cache-Control: public,max-age=3600");
  //if its an options request you don't need to proceed past CORS request.
  if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    die();
  }
}

Answer 3

If you want wildcard domain, i think this is more efficient

if(isset($_SERVER['HTTP_ORIGIN']) && preg_match('!^http(s)?://([a-z0-9\-]+\.)?example.com$!is', $_SERVER['HTTP_ORIGIN']))
{
    header('Access-Control-Allow-Origin: '.$_SERVER['HTTP_ORIGIN']);
}

Answer 4

While the answer works, it does defeat the purpose of the whole thing, since it allows requests from any host.

I use something like:

if(isset($_SERVER['HTTP_ORIGIN'])) {
  $origin = $_SERVER['HTTP_ORIGIN'];
  if($origin == 'https://sub1.my-website.com' OR $origin == 'https://sub2.my-website.com') {
    header("Access-Control-Allow-Origin: $origin");
  }
}

Answer 5

The solution to this issue is to use the $_SERVER['HTTP_ORIGIN'] variable to determine whether the request has come from an allowed domain, and then conditionally set the Access-Control-Allow-Origin like so:

$allowed_domains = [/* Array of allowed domains*/];

if (in_array($_SERVER['HTTP_ORIGIN'], $allowed_domains)) {
    header('Access-Control-Allow-Origin: ' . $_SERVER['HTTP_ORIGIN']);
}

Answer 6

This was my challenge and solution:

1 - Backend PHP on api.example.com.

2 - Multiple JS front ends such as one.example.com, two.example.com etc.

3 - Cookies needed to be passed both ways.

4 - AJAX call from multiple front-ends to PHP backend on api.example.com

5 - In PHP, I do not prefer to use $_SERVER["HTTP_ORIGIN"], not always reliable/safe in my opinion (I had some browsers where HTTP-ORIGIN was always empty).

The normal way to do this in PHP with single front end domain is starting PHP code with:

header('Access-Control-Allow-Origin: https://one.example.com');  
header('Access-Control-Allow-Headers: Origin, Content-Type, X-Auth-Token');  
header('Access-Control-Allow-Credentials: true');  

And in JS on one.example.com domain:

jQuery.ajax({
    url: myURL,
    type: "POST",
    xhrFields: {withCredentials: true},
    dataType: "text",
    contentType: "text/xml; charset=\"utf-8\"",
    cache: false,
    headers: "",
    data: myCallJSONStr,
    success: function(myResponse) {.....}

However, this is not workable as I am using multiple subdomains to call my API domain.

And this solution will NOT work as I want to pass on cookies:

header('Access-Control-Allow-Origin: *');  

It conflicts with the pass on cookie setting on the JS site:

xhrFields: {withCredentials: true}

Here is what I did:

1 - use GET parameter to pass the Subdomain. 2 - Hardcode the Main domain in PHP so only (all) Subdomains are allowed.

This is the JS/JQuery AJAX part of my solution:

function getSubDomain(){
    
    let mySubDomain = "";
    
    let myDomain = window.location.host;
    let myArrayParts = myDomain.split(".");
    if (myArrayParts.length == 3){
        mySubDomain = myArrayParts[0];
    }
    
    return mySubDomain;
    
}

And in the AJAX call:

    let mySubDomain = getSubDomain();
    if (mySubDomain != ""){
        myURL += "?source=" + mySubDomain + "&end"; //use & instead of ? if URL already has GET parameters
    }
    
    jQuery.ajax({
        url: myURL,
        type: "POST",
        xhrFields: {withCredentials: true},
        dataType: "text",
        contentType: "text/xml; charset=\"utf-8\"",
        cache: false,
        headers: "",
        data: myCallJSONStr,
        success: function(myResponse) {.....}

Finally, the PHP part:

<?php

$myDomain = "example.com";
$mySubdomain = "";

if (isset($_GET["source"])) {
    $mySubdomain = $_GET["source"].".";
}

$myDomainAllowOrigin = "https://".$mySubdomain.$myDomain;
$myAllowOrigin = "Access-Control-Allow-Origin: ".$myDomainAllowOrigin;

//echo $myAllowOrigin;

header($myAllowOrigin);  
header('Access-Control-Allow-Headers: Origin, Content-Type, X-Auth-Token');  
header('Access-Control-Allow-Credentials: true');

IMPORTANT, don't forget to set the cookies for all subdomains, in this case the domain for the cookie would be: .example.com (so with a dot in front of the main domain):

<?php

    //////////////// GLOBALS /////////////////////////////////
    
    $gCookieDomain = ".example.com";
    $gCookieValidForDays = 90;
    
    //////////////// COOKIE FUNTIONS /////////////////////////////////
    
    function setAPCookie($myCookieName, $myCookieValue, $myHttponly){
        global $gCookieDomain;
        global $gCookieValidForDays;
        
        $myExpires = time()+60*60*24*$gCookieValidForDays;
        setcookie($myCookieName, $myCookieValue, $myExpires, "/", $gCookieDomain, true, $myHttponly);   
        
        return $myExpires;
    }

This solution allows me to call the API on api.example.com from any subdomains on example.com.

NB. for situation where there is only a single calling subdomain, I prefer using .htaccess for setting CORS instead of PHP. Here is an example of .htaccess (linux/apache) for only one.example.com calling api.example.com:

<IfModule mod_headers.c>
    Header set Access-Control-Allow-Origin "https://one.example.com"
    Header set Access-Control-Allow-Headers "Origin, Content-Type, X-Auth-Token"
    Header set Access-Control-Allow-Credentials "true"
</IfModule>

And place this .htaccess in the root of api.example.com.