code: @Override
      public GetChangeTokenResult getChangeToken(GetChangeTokenRequest request) {
          request = beforeClientExecution(request);
          return executeGetChangeToken(request);
      }
docs: <p>
  When you want to create, update, or delete AWS WAF objects, get a change token and include the change token in
  the create, update, or delete request. Change tokens ensure that your application doesn't submit conflicting
  requests to AWS WAF.
  </p>
  <p>
  Each create, update, or delete request must use a unique change token. If your application submits a
  <code>GetChangeToken</code> request and then submits a second <code>GetChangeToken</code> request before
  submitting a create, update, or delete request, the second <code>GetChangeToken</code> request returns the same
  value as the first <code>GetChangeToken</code> request.
  </p>
  <p>
  When you use a change token in a create, update, or delete request, the status of the change token changes to
  <code>PENDING</code>, which indicates that AWS WAF is propagating the change to all AWS WAF servers. Use
  <code>GetChangeTokenStatus</code> to determine the status of your change token.
  </p>
  
  @param getChangeTokenRequest
  @return Result of the GetChangeToken operation returned by the service.
  @throws WAFInternalErrorException
  The operation failed because of a system problem, even though the request was valid. Retry your request.
  @sample AWSWAFRegional.GetChangeToken
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/waf-regional-2016-11-28/GetChangeToken" target="_top">AWS
  API Documentation</a>