r response with a <code>Retry-After</code> header set to the value provided by the method
 parameter.
 </p>
 <p>
 Invoking a <code>cancel(...)</code> method multiple times to cancel request processing has the same
 effect as canceling the request processing only once. Invoking a <code>cancel(...)</code> method on
 an asynchronous response instance that has already been cancelled or resumed has no effect and the
 method call is ignored while returning <code>true</code>, in case the request has been cancelled