added async signing

index.js

@@ -35,7 +35,7 @@ JWT.decode = function (jwt, options) {
   return payload;
 };
 
-JWT.sign = function(payload, secretOrPrivateKey, options) {
+JWT.sign = function(payload, secretOrPrivateKey, options, callback) {
   options = options || {};
 
   var header = {};
@@ -79,9 +79,16 @@ JWT.sign = function(payload, secretOrPrivateKey, options) {
     encoding = options.encoding;
   }
 
-  var signed = jws.sign({header: header, payload: payload, secret: secretOrPrivateKey, encoding: encoding});
-
-  return signed;
+  if(typeof callback === 'function') {
+    jws.createSign({
+      header: header,
+      payload: payload,
+      privateKey: secretOrPrivateKey,
+      payload: JSON.stringify(payload)
+    }).on('done', callback);
+  } else {
+    return jws.sign({header: header, payload: payload, secret: secretOrPrivateKey, encoding: encoding});
+  }
 };
 
 JWT.verify = function(jwtString, secretOrPublicKey, options, callback) {

test/async_sign.tests.js

@@ -0,0 +1,20 @@
+var jwt = require('../index');
+
+var expect = require('chai').expect;
+
+describe('signing a token asynchronously', function() {
+
+  describe('when signing a token', function() {
+    var secret = 'shhhhhh';
+    var syncToken = jwt.sign({ foo: 'bar' }, secret, { algorithm: 'HS256' });
+
+    it('should return the same result as singing synchronously', function(done) {
+      jwt.sign({ foo: 'bar' }, secret, { algorithm: 'HS256' }, function (asyncToken) {
+        expect(asyncToken).to.be.a('string');
+        expect(asyncToken.split('.')).to.have.length(3);
+        expect(asyncToken).to.equal(syncToken);
+        done();
+      });
+    });
+  });
+});