support grant specific access token ttl

src/Grant/AbstractGrant.php

@@ -80,6 +80,19 @@ abstract class AbstractGrant implements GrantTypeInterface
         return $this->responseType;
     }
 
+    /**
+     * Get the TTL for an access token
+     * @return int The TTL
+     */
+    public function getAccessTokenTTL()
+    {
+        if ($this->accessTokenTTL) {
+            return $this->accessTokenTTL;
+        }
+
+        return $this->server->getAccessTokenTTL();
+    }
+
     /**
      * Override the default access token expire time
      * @param  int  $accessTokenTTL