Como gerar o HMAC da cadeia de caracteres que usa elementos definidos da solicitação HTTP/HTTPS, usando Java

package sample;
import com.glide.util;
import java.security.SignatureException;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

public class AuthUtil {
	
private static final String HMAC_SHA1_ALGORITHM = "HmacSHA1";

/***
 * Generates base64-encode the HMAC(Hash Message Authentication Code) of input data
 * 
 * @param data
 * @param key
 * @return
 * @throws java.security.SignatureException
 */
public static String signData(String data, String key) throws java.security.SignatureException {
	String result;
	try {
		// get an hmac_sha1 key from the raw key bytes
		SecretKeySpec signingKey = new SecretKeySpec(key.getBytes(), HMAC_SHA1_ALGORITHM);

		// create hmac_sha1 Mac instance and initialize with the signing key
		Mac = Mac.getInstance(HMAC_SHA1_ALGORITHM);
		mac.init(signingKey);

		// compute the hmac on input data bytes
		byte[] rawHmac = mac.doFinal(data.getBytes("UTF-8"));

		// base64-encode the hmac
		result = Base64.encode(rawHmac);

	} catch (Exception e) {
		throw new SignatureException("Failed to generate HMAC : " + e.getMessage());
	}
	return result;
}
}