default void verifySignedRequest(RestRequest restRequest, Callback<Void> callback) {
    Exception exception = null;
    try {
      verifySignedRequest(restRequest);
    } catch (Exception e) {
      exception = e;
    } finally {
      callback.onCompletion(null, exception);
    }
  }
Verifies that the signature in {@code restRequest} is valid. Any remote calls in the implementation should be made
asynchronously.
@param restRequest the {@link RestRequest} to check.
@param callback the {@link Callback} that will be called after signature verification.
ambry-api/src/main/java/com/github/ambry/frontend/UrlSigningService.java