diff --git a/website/src/controllers/groups.js b/website/src/controllers/groups.js
index 126858c6ac..6ce43e2be3 100644
--- a/website/src/controllers/groups.js
+++ b/website/src/controllers/groups.js
@@ -18,6 +18,7 @@ var isProd = nconf.get('NODE_ENV') === 'production';
 var api = module.exports;
 var pushNotify = require('./pushNotifications');
 var analytics = utils.analytics;
+var firebase = require('../libs/firebase');
 
 /*
   ------------------------------------------------------------------------
@@ -190,7 +191,10 @@ api.create = function(req, res, next) {
     async.waterfall([
       function(cb){user.save(cb)},
       function(saved,ct,cb){group.save(cb)},
-      function(saved,ct,cb){saved.populate('members',nameFields,cb)}
+      function(saved,ct,cb){
+        firebase.addUserToGroup(saved._id, user._id);
+        saved.populate('members', nameFields, cb);
+      }
     ],function(err,saved){
       if (err) return next(err);
       res.json(saved);
@@ -207,6 +211,7 @@ api.create = function(req, res, next) {
         group.save(cb);
       },
       function(saved, count, cb){
+        firebase.addUserToGroup(saved._id, user._id);
         saved.populate('members', nameFields, cb);
       }
     ], function(err, populated){
@@ -479,6 +484,8 @@ api.join = function(req, res, next) {
       group.save(cb);
     },
     function(cb){
+      firebase.addUserToGroup(group._id, user._id);
+      // TODO why query group once again?
       populateQuery(group.type, Group.findById(group._id)).exec(cb);
     }
   ], function(err, results){
diff --git a/website/src/libs/firebase.js b/website/src/libs/firebase.js
index 3fc302fccb..958393cf6a 100644
--- a/website/src/libs/firebase.js
+++ b/website/src/libs/firebase.js
@@ -8,9 +8,37 @@ var firebaseConfig = nconf.get('FIREBASE');
 if(isProd){
   firebaseRef = new Firebase('https://' + firebaseConfig.APP + '.firebaseio.com');
 
-  firebaseRef.on('value', function(snapshot){
-    console.log(snapshot.val());
+  firebaseRef.authWithCustomToken(firebaseConfig.SECRET, function(err, authData){
+    // TODO it's ok to kill the server here? what if FB is offline?
+    if(err) throw new Error('Impossible to authenticate Firebase');
   });
 }
 
-var api = module.exports = {};
\ No newline at end of file
+var api = module.exports = {};
+
+api.addUserToGroup = function(groupId, userId){
+  if(!isProd) return;
+
+  // TODO is throw ok? we don't have callbacks
+  if(!userId || !groupId) throw new Error('groupId, userId are required.');
+
+  firebaseRef.child('members/' + groupId + '/' + userId)
+    .set(true);
+
+  firebaseRef.child('users/' + userId + '/' + groupId)
+    .set(true);
+};
+
+api.removeUserFromGroup = function(groupId, userId){
+  if(!isProd) return;
+
+  if(!userId || !groupId) throw new Error('groupId, userId are required.');
+
+  firebaseRef.child('members/' + groupId + '/' + userId)
+    .set(false);
+
+  firebaseRef.child('users/' + userId + '/' + groupId)
+    .set(false);
+};
+
+api.userLeaves
\ No newline at end of file
diff --git a/website/src/models/group.js b/website/src/models/group.js
index 56d64f6ec2..6c57b08168 100644
--- a/website/src/models/group.js
+++ b/website/src/models/group.js
@@ -5,6 +5,7 @@ var _ = require('lodash');
 var async = require('async');
 var logging = require('../logging');
 var Challenge = require('./../models/challenge').model;
+var firebase = require('../libs/firebase');
 
 // NOTE any change to groups' members in MongoDB will have to be run through the API
 // changes made directly to the db will cause Firebase to get out of sync
@@ -444,7 +445,12 @@ GroupSchema.methods.leave = function(user, keep, mainCb){
         Group.update({_id:group._id}, update, cb);
       }
     }
-  ], mainCb);
+  ], function(err){
+    if(err) return mainCb(err);
+
+    firebase.removeUserFromGroup(group._id, user._id);
+    return mainCb();
+  });
 };