How to generate a SharedAccessSignature for the Azure Queue REST API

import java.nio.charset.StandardCharsets;

import java.util.Calendar;

import javax.crypto.Mac;

import javax.crypto.spec.SecretKeySpec;

import org.mule.modules.microsoftservicebus.utils.ServiceBusUtils;

import org.mule.util.Base64;

/**

 * RESTful calls to an Azure Queue Service must be authorized. This class

 * generates a SharedAccessSignature that can be used as the Authorization

 * header of the REST call.

 * <p>

 * Example - View all the queues

 * <pre>

 * GET /$Resources/Queues?api-version=2015-01 HTTP/1.1

 * Host: MY_NAMESPACE.servicebus.windows.net

 * Authorization: SharedAccessSignature sr=https://MY_NAMESPACE.servicebus.windows.net&sig=OfdrmxrugTKQA240Zi59u9vxmQx88NPzf%2besFuqTVM4%3d&se=1440367081&skn=RootManageSharedAccessKey

 * </pre>

 * <p>

 * Example - View the messages on a queue

 * <pre>

 * GET /intervals/messages?api-version=2015-01 HTTP/1.1

 * Host: MY_NAMESPACE.servicebus.windows.net

 * Authorization: SharedAccessSignature sr=https://MY_NAMESPACE.servicebus.windows.net&sig=OfdrmxrugTKQA240Zi59u9vxmQx88NPzf%2besFuqTVM4%3d&se=1440367081&skn=RootManageSharedAccessKey

 * </pre>

 * <p>

 * Example - View the messages on a queue's DeadLetterQueue

 * <pre>

 * GET /intervals/$DeadLetterQueue/messages?api-version=2015-01 HTTP/1.1

 * Host: MY_NAMESPACE.servicebus.windows.net

 * Authorization: SharedAccessSignature sr=https://MY_NAMESPACE.servicebus.windows.net&sig=OfdrmxrugTKQA240Zi59u9vxmQx88NPzf%2besFuqTVM4%3d&se=1440367081&skn=RootManageSharedAccessKey

 * </pre>

 *

 */

public class RestApiUtil {

       public static String generateSharedAccessSignature(String url, String keyName, String key) throws Exception {

             String sasToken = "";

             String encodedUrl = ServiceBusUtils.urlEncodeLowerCase(url);

             Calendar calendar = Calendar.getInstance();

             calendar.add(Calendar.HOUR, 1);

             Long expiry = Long.valueOf(calendar.getTimeInMillis() / 1000L);

             String stringToSign = (new StringBuilder()).append(encodedUrl).append("\n").append(expiry).toString();

             Mac mac = Mac.getInstance("HmacSHA256");

             SecretKeySpec signingKey = new SecretKeySpec(key.getBytes(StandardCharsets.UTF_8), mac.getAlgorithm());

             mac.init(signingKey);

             String signature = Base64.encodeBytes(mac.doFinal(stringToSign.getBytes(StandardCharsets.UTF_8)));

             sasToken = String.format("SharedAccessSignature sr=%s&sig=%s&se=%s&skn=%s", new Object[] { encodedUrl,

                           ServiceBusUtils.urlEncodeLowerCase(signature), expiry, keyName });

             return sasToken;

       }

       public static void main(String... args) throws Exception {

             String url = "https://MY_NAMESPACE.servicebus.windows.net";

             String keyName = "RootManageSharedAccessKey";

             String key = "2ZOcYrXxx/H33+LyhxJQ24yKkW4+zw6KY6w90z+p+4k=";

             String token = RestApiUtil.generateSharedAccessSignature(url, keyName, key);

             System.out.println("-- Authorization header --");

             System.out.println(token);

       }

}