gistfile1.java

//Some necessary imports
import java.net.URLEncoder;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import org.apache.commons.codec.binary.Hex;

...


public static String generateTypekitPreviewSignature(String apiToken, String apiTokenPublicId, String host, long timeToExpire){
  try{
    String DELIM= "\n";
    long expiration = (System.currentTimeMillis()/1000) + timeToExpire;
    StringBuilder raw = new StringBuilder("");
    raw.append(apiTokenPublicId).append(DELIM).append("endpoint=/previewkits").append(DELIM).append("referrer=" + host).append(DELIM).append("time=" + Long.toString(expiration));
    String toSign = raw.toString();
    String sig = hmacsha256(apiToken, toSign);

    StringBuilder result = new StringBuilder("");
    result.append("1").append(DELIM).append(toSign).append(DELIM).append(sig);
    return URLEncoder.encode(result.toString(), "UTF-8");
  }catch(Exception e){ //unsupportedencoding, invalidkey, nosuchalgorithm
    log.error("Couldn't generate typekit signature", e); 
    return null; 
  }   
}

public static String hmacsha256(String key, String toSign){
  try{
    SecretKeySpec signingkey = new SecretKeySpec(key.getBytes(), "HmacSha256");
    Mac mac = Mac.getInstance("HmacSha256");
    mac.init(signingkey);
    byte[] rawhmac = mac.doFinal(toSign.getBytes());
    return new String(Hex.encodeHex(rawhmac));
  } catch(Exception e){ //invalidkey, nosuchalgorithm - never gonna happen)
    log.error("Couldn't generate hmacsha256", e); 
    return null;
  }   
}