code: public com.squareup.okhttp.Call getHeadersAsync(final ApiCallback<Map<String, String>> callback)
              throws ApiException {
  
          com.squareup.okhttp.Call call = getHeadersValidateBeforeCall(callback);
          Type localVarReturnType = new TypeToken<Map<String, String>>() {
          }.getType();
          apiClient.executeAsync(call, localVarReturnType, callback);
          return call;
      }
docs: Debug request headers (asynchronously) Echo the request headers for
  debugging purposes. Note that the &#39;Connection&#39; header and any
  &#39;X-&#39; headers are not included
  
  @param callback
  The callback to be executed when the API call finishes
  @return The request call
  @throws ApiException
  If fail to process the API call, e.g. serializing the request
  body object