signed.addHeader("Visa");
MultivaluedMapImpl<String, String> headers = new MultivaluedMapImpl<String, String>();
headers.add("Visa", "v1");
headers.add("Visa", "v2");
headers.add("Visa", "v3");
signed.sign(headers, null, keys.getPrivate());
String signedHeader = signed.toString();
System.out.println(signedHeader);