Allow setting the Referer header

src/Connection.php

@@ -24,7 +24,7 @@
  */
 class Connection
 {
-    public const VERSION = '3.0.1';
+    public const VERSION = '3.1.0';
 
     public const BASE_URL = 'https://app.sendy.nl';
 
@@ -60,6 +60,9 @@ class Connection
     /** @var string The appendix for the user agent */
     private string $userAgentAppendix = '';
 
+    /** @var string|null The URL of the application or website using this SDK, sent as the Referer header */
+    private ?string $referer = null;
+
     /** @var mixed */
     private $state = null;
 
@@ -96,6 +99,13 @@ public function setUserAgentAppendix(string $userAgentAppendix): Connection
         return $this;
     }
 
+    public function setReferer(?string $referer): Connection
+    {
+        $this->referer = $referer;
+
+        return $this;
+    }
+
     public function setClientId(string $clientId): Connection
     {
         $this->clientId = $clientId;
@@ -295,6 +305,10 @@ public function createRequest(
             'User-Agent' => trim($userAgent),
         ]);
 
+        if ($this->referer !== null) {
+            $headers['Referer'] = $this->referer;
+        }
+
         if (! empty($params)) {
             $endpoint .= strpos($endpoint, '?') === false ? '?' : '&';
             $endpoint .= http_build_query($params);

tests/ConnectionTest.php

@@ -46,6 +46,19 @@ public function testUserAgentIsSet(): void
         );
     }
 
+    public function testRefererIsSet(): void
+    {
+        $connection = $this->createConnection();
+        $this->assertArrayNotHasKey('referer', $connection->createRequest('GET', '/')->getHeaders());
+
+        $connection = $this->createConnection();
+        $connection->setReferer('https://example.com');
+        $this->assertEquals(
+            'https://example.com',
+            $connection->createRequest('GET', '/')->getHeaders()['referer'],
+        );
+    }
+
     public function testTokenExpires(): void
     {
         $connection = new Connection();