diff --git a/src/GoogleStorageAdapter.php b/src/GoogleStorageAdapter.php
index 26b9460..5d651b3 100644
--- a/src/GoogleStorageAdapter.php
+++ b/src/GoogleStorageAdapter.php
@@ -27,6 +27,11 @@ class GoogleStorageAdapter extends AbstractAdapter
      */
     protected $bucket;
 
+    /**
+     * @var array
+     */
+    protected $auth = [];
+
     /**
      * @var string
      */
@@ -38,7 +43,7 @@ class GoogleStorageAdapter extends AbstractAdapter
      * @param string $pathPrefix
      * @param string $storageApiUri
      */
-    public function __construct(StorageClient $storageClient, Bucket $bucket, $pathPrefix = null, $storageApiUri = null)
+    public function __construct(StorageClient $storageClient, Bucket $bucket, $pathPrefix = null, $storageApiUri = null, $key_file_path = '')
     {
         $this->storageClient = $storageClient;
         $this->bucket = $bucket;
@@ -50,6 +55,12 @@ public function __construct(StorageClient $storageClient, Bucket $bucket, $pathP
         if ($storageApiUri) {
             $this->storageApiUri = $storageApiUri;
         }
+
+        if (is_file($key_file_path)) {
+            if ($data = json_decode(file_get_contents($key_file_path), True)) {
+                $this->auth = $data;
+            }
+        }
     }
 
     /**
@@ -380,6 +391,45 @@ public function getUrl($path)
         return $uri . '/' . $this->bucket->name() . '/' . $path;
     }
 
+    /**
+     * Return a signed url to a file with expiration timestamp.
+     *
+     * @param string $path
+     * @param integer $expires
+     * @param string $method
+     * @return string
+     */
+    public function getSignedUrl($path, $expires = 0, $method = 'GET')
+    {
+        if (!empty($this->auth)) {
+            $signature = '';
+            $canonical_resource = '/' . $this->bucket->name() . '/' . $path; // e.g.: /bucket/somefile.txt
+
+            $to_sign = [
+                $method,
+                '',
+                '',
+                $expires,
+                $canonical_resource
+            ];
+
+            $to_sign_string = implode("\n", $to_sign);
+
+            // sign $to_sign_string as $signature with private_key from provided
+            openssl_sign($to_sign_string, $signature, $this->auth['private_key'], 'sha256');
+
+            $signature = urlencode(base64_encode($signature));
+
+            return $this->getStorageApiUri()
+            . $canonical_resource
+            . "?GoogleAccessId=" . urlencode($this->auth['client_email'])
+            . "&Expires=" . $expires
+            . "&Signature=" . $signature;
+        }
+
+        return $this->getUrl($path);
+    }
+
     /**
      * @param string $path
      * @return string