@Override
    public void addHeader(String headerName, String headerValue) {
        headers.add(headerName, headerValue);
    }
@see io.apiman.gateway.engine.components.http.IHttpClientRequest#addHeader(java.lang.String, java.lang.String)
gateway/platforms/servlet/src/main/java/io/apiman/gateway/platforms/servlet/components/HttpClientRequestImpl.java