Add save_access_token event to allow saving the access token.

For some reason, people might want to save the generated access token in
a database, so the save_access_token event is now emitted. It is
optional.

Closes ammmir#10

examples/simple.js

@@ -67,6 +67,11 @@ myOAP.on('create_access_token', function(user_id, client_id, next) {
   next(data);
 });
 
+// (optional) do something with the generated access token
+myOAP.on('save_access_token', function(user_id, client_id, access_token) {
+  console.log('saving access token %s for user_id=%s client_id=%s', access_token, user_id, client_id);
+});
+
 // an access token was received in a URL query string parameter or HTTP header
 myOAP.on('access_token', function(req, token, next) {
   var TOKEN_TTL = 10 * 60 * 1000; // 10 minutes

index.js

@@ -116,7 +116,12 @@ OAuth2Provider.prototype.oauth = function() {
           }
 
           self.emit('create_access_token', user_id, client_id, function(extra_data) {
-            url += querystring.stringify(self.generateAccessToken(user_id, client_id, extra_data));
+            var atok = self.generateAccessToken(user_id, client_id, extra_data);
+
+            if(self.listeners('save_access_token').length > 0)
+              self.emit('save_access_token', user_id, client_id, atok);
+
+            url += querystring.stringify(atok);
 
             res.writeHead(303, {Location: url});
             res.end();
@@ -161,6 +166,11 @@ OAuth2Provider.prototype.oauth = function() {
         res.writeHead(200, {'Content-type': 'application/json'});
 
         self.emit('create_access_token', user_id, client_id, function(extra_data) {
+          var atok = self.generateAccessToken(user_id, client_id, extra_data);
+
+          if(self.listeners('save_access_token').length > 0)
+            self.emit('save_access_token', user_id, client_id, atok);
+
           res.end(JSON.stringify(self.generateAccessToken(user_id, client_id, extra_data)));
         });