diff --git a/src/components/NavigationBar.vue b/src/components/NavigationBar.vue
index d3fc4a49..6821f6c1 100644
--- a/src/components/NavigationBar.vue
+++ b/src/components/NavigationBar.vue
@@ -11,7 +11,7 @@
       </button>
     </div>
     <div class="navigation-bar__inner navigation-bar__inner--right flex flex--row">
-      <div class="navigation-bar__spinner">
+      <div class="navigation-bar__spinner" v-show="showSpinner">
         <div class="spinner"></div>
       </div>
       <div class="navigation-bar__title navigation-bar__title--fake text-input"></div>
@@ -75,6 +75,9 @@ export default {
     ...mapGetters('layout', [
       'styles',
     ]),
+    showSpinner() {
+      return !this.$store.state.queue.isEmpty;
+    },
     titleWidth() {
       if (!this.mounted) {
         return 0;
diff --git a/src/components/SideBar.vue b/src/components/SideBar.vue
index f55e7b06..7f4c1e0e 100644
--- a/src/components/SideBar.vue
+++ b/src/components/SideBar.vue
@@ -13,16 +13,16 @@
     </div>
     <div class="side-bar__inner">
       <div v-if="panel === 'menu'" class="side-bar__panel side-bar__panel--menu">
-        <side-bar-item @click.native="signin">
+        <side-bar-item v-if="!loginToken" @click.native="signin">
           <icon-login slot="icon"></icon-login>
           <div>Sign in with Google</div>
           <span>Have all your files and settings backed up and synced.</span>
         </side-bar-item>
-        <side-bar-item @click.native="signin">
-          <icon-login slot="icon"></icon-login>
-          <div>Sign in on CouchDB</div>
-          <span>Save and collaborate on a CouchDB hosted by you.</span>
-        </side-bar-item>
+        <!-- <side-bar-item @click.native="signin">
+                <icon-login slot="icon"></icon-login>
+                <div>Sign in on CouchDB</div>
+                <span>Save and collaborate on a CouchDB hosted by you.</span>
+              </side-bar-item> -->
         <side-bar-item @click.native="panel = 'toc'">
           <icon-toc slot="icon"></icon-toc>
           Table of contents
@@ -44,12 +44,13 @@
 </template>
 
 <script>
-import { mapActions } from 'vuex';
+import { mapGetters, mapActions } from 'vuex';
 import Toc from './Toc';
 import SideBarItem from './SideBarItem';
 import markdownSample from '../data/markdownSample.md';
 import markdownConversionSvc from '../services/markdownConversionSvc';
-import userSvc from '../services/userSvc';
+import googleHelper from '../services/helpers/googleHelper';
+import syncSvc from '../services/syncSvc';
 
 const panelNames = {
   menu: 'Menu',
@@ -72,6 +73,9 @@ export default {
     markdownSample: markdownConversionSvc.highlight(markdownSample),
   }),
   computed: {
+    ...mapGetters('data', [
+      'loginToken',
+    ]),
     panelName() {
       return panelNames[this.panel];
     },
@@ -81,7 +85,10 @@ export default {
       'toggleSideBar',
     ]),
     signin() {
-      userSvc.signinWithGoogle();
+      googleHelper.startOauth2([
+        'openid',
+        'https://www.googleapis.com/auth/drive.appdata',
+      ]).then(() => syncSvc.requestSync());
     },
   },
 };
@@ -111,6 +118,10 @@ export default {
   left: 1000px;
 }
 
+.side-bar__panel--menu {
+  padding: 5px;
+}
+
 .side-bar__panel--help {
   padding: 0 10px 40px 20px;
 
diff --git a/src/components/SideBarItem.vue b/src/components/SideBarItem.vue
index 5f991512..c59f183f 100644
--- a/src/components/SideBarItem.vue
+++ b/src/components/SideBarItem.vue
@@ -14,7 +14,6 @@
   text-align: left;
   padding: 10px 12px;
   height: auto;
-  margin: 5px;
 
   span {
     display: inline-block;
diff --git a/src/index.js b/src/index.js
index ad4bde94..91b1efac 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,6 +1,5 @@
 import Vue from 'vue';
 import './extensions/';
-import './services/syncSvc';
 import './services/optional';
 import './icons/';
 import App from './components/App';
diff --git a/src/services/helpers/googleHelper.js b/src/services/helpers/googleHelper.js
new file mode 100644
index 00000000..cdfd9bed
--- /dev/null
+++ b/src/services/helpers/googleHelper.js
@@ -0,0 +1,224 @@
+import utils from '../utils';
+import store from '../../store';
+
+const clientId = '241271498917-t4t7d07qis7oc0ahaskbif3ft6tk63cd.apps.googleusercontent.com';
+const appsDomain = null;
+const tokenExpirationMargin = 10 * 60 * 1000; // 10 min
+
+// const scopeMap = {
+//   profile: [
+//     'https://www.googleapis.com/auth/userinfo.profile',
+//   ],
+//   gdrive: [
+//     'https://www.googleapis.com/auth/drive.install',
+//     store.getters['data/settings'].gdriveFullAccess === true ?
+//     'https://www.googleapis.com/auth/drive' :
+//     'https://www.googleapis.com/auth/drive.file',
+//   ],
+//   blogger: [
+//     'https://www.googleapis.com/auth/blogger',
+//   ],
+//   picasa: [
+//     'https://www.googleapis.com/auth/photos',
+//   ],
+// };
+
+const request = (googleToken, options) => utils.request({
+  ...options,
+  headers: {
+    ...options.headers,
+    Authorization: `Bearer ${googleToken.accessToken}`,
+  },
+});
+
+const saveFile = (googleToken, data, appData) => {
+  const options = {
+    method: 'POST',
+    url: 'https://www.googleapis.com/upload/drive/v2/files',
+    headers: {},
+  };
+  if (appData) {
+    options.method = 'PUT';
+    options.url = `https://www.googleapis.com/drive/v2/files/${appData.id}`;
+    options.headers['if-match'] = appData.etag;
+  }
+  const metadata = {
+    title: data.name,
+    parents: [{
+      id: 'appDataFolder',
+    }],
+    properties: Object.keys(data)
+      .filter(key => key !== 'name' && key !== 'tx')
+      .map(key => ({
+        key,
+        value: JSON.stringify(data[key]),
+        visibility: 'PUBLIC',
+      })),
+  };
+  const media = null;
+  const boundary = `-------${utils.uid()}`;
+  const delimiter = `\r\n--${boundary}\r\n`;
+  const closeDelimiter = `\r\n--${boundary}--`;
+  if (media) {
+    let multipartRequestBody = '';
+    multipartRequestBody += delimiter;
+    multipartRequestBody += 'Content-Type: application/json\r\n\r\n';
+    multipartRequestBody += JSON.stringify(metadata);
+    multipartRequestBody += delimiter;
+    multipartRequestBody += 'Content-Type: application/json\r\n\r\n';
+    multipartRequestBody += JSON.stringify(media);
+    multipartRequestBody += closeDelimiter;
+    return request(googleToken, {
+      ...options,
+      params: {
+        uploadType: 'multipart',
+      },
+      headers: {
+        ...options.headers,
+        'Content-Type': `multipart/mixed; boundary="${boundary}"`,
+      },
+      body: multipartRequestBody,
+    });
+  }
+  return request(googleToken, {
+    ...options,
+    body: metadata,
+  }).then(res => ({
+    id: res.body.id,
+    etag: res.body.etag,
+  }));
+};
+
+export default {
+  startOauth2(scopes, sub = null, silent = false) {
+    return utils.startOauth2(
+        'https://accounts.google.com/o/oauth2/v2/auth', {
+          client_id: clientId,
+          response_type: 'token',
+          scope: scopes.join(' '),
+          hd: appsDomain,
+          login_hint: sub,
+          prompt: silent ? 'none' : null,
+        }, silent)
+      // Call the tokeninfo endpoint
+      .then(data => utils.request({
+        method: 'POST',
+        url: 'https://www.googleapis.com/oauth2/v3/tokeninfo',
+        params: {
+          access_token: data.accessToken,
+        },
+      }).then((res) => {
+        // Check the returned client ID consistency
+        if (res.body.aud !== clientId) {
+          throw new Error('Client ID inconsistent.');
+        }
+        // Check the returned sub consistency
+        if (sub && res.body.sub !== sub) {
+          throw new Error('Google account ID not expected.');
+        }
+        // Build token object including scopes and sub
+        return {
+          scopes,
+          accessToken: data.accessToken,
+          expiresOn: Date.now() + (data.expiresIn * 1000),
+          sub: res.body.sub,
+          isLogin: !store.getters['data/loginToken'],
+        };
+      }))
+      // Call the tokeninfo endpoint
+      .then(googleToken => request(googleToken, {
+        method: 'GET',
+        url: 'https://www.googleapis.com/plus/v1/people/me',
+      }).then((res) => {
+        // Add name to googleToken
+        googleToken.name = res.body.displayName;
+        const existingToken = store.getters['data/googleTokens'][googleToken.sub];
+        if (existingToken) {
+          if (!sub) {
+            throw new Error('Google account already linked.');
+          }
+          // Add isLogin and lastChangeId to googleToken
+          googleToken.isLogin = existingToken.isLogin;
+          googleToken.lastChangeId = existingToken.lastChangeId;
+        }
+        // Add googleToken to googleTokens
+        store.dispatch('data/setGoogleToken', googleToken);
+        return googleToken;
+      }));
+  },
+  refreshToken(scopes, googleToken) {
+    const sub = googleToken.sub;
+    const lastToken = store.getters['data/googleTokens'][sub];
+    const mergedScopes = [...new Set([
+      ...scopes,
+      ...lastToken.scopes,
+    ])];
+
+    return Promise.resolve()
+      .then(() => {
+        if (mergedScopes.length === lastToken.scopes.length) {
+          return lastToken;
+        }
+        // New scopes are requested, popup an authorize window
+        return this.startOauth2(mergedScopes, sub);
+      })
+      .then((refreshedToken) => {
+        if (refreshedToken.expiresOn > Date.now() + tokenExpirationMargin) {
+          // Token is fresh enough
+          return refreshedToken;
+        }
+        // Token is almost outdated, try to take one in background
+        return this.startOauth2(mergedScopes, sub, true)
+          // If it fails try to popup a window
+          .catch(() => this.startOauth2(mergedScopes, sub));
+      });
+  },
+  getChanges(googleToken) {
+    let changes = [];
+    return this.refreshToken(['https://www.googleapis.com/auth/drive.appdata'], googleToken)
+      .then((refreshedToken) => {
+        const lastChangeId = refreshedToken.lastChangeId || 0;
+        const getPage = pageToken => request(refreshedToken, {
+          method: 'GET',
+          url: 'https://www.googleapis.com/drive/v2/changes',
+          params: {
+            pageToken,
+            startChangeId: pageToken || !lastChangeId ? null : lastChangeId + 1,
+            spaces: 'appDataFolder',
+            fields: 'nextPageToken,items(deleted,file/id,file/etag,file/title,file/properties(key,value))',
+          },
+        }).then((res) => {
+          changes = changes.concat(res.body.items);
+          if (res.body.nextPageToken) {
+            return getPage(res.body.nextPageToken);
+          }
+          return changes;
+        });
+
+        return getPage();
+      });
+  },
+  updateLastChangeId(googleToken, changes) {
+    const refreshedToken = store.getters['data/googleTokens'][googleToken.sub];
+    let lastChangeId = refreshedToken.lastChangeId || 0;
+    changes.forEach((change) => {
+      if (change.id > lastChangeId) {
+        lastChangeId = change.id;
+      }
+    });
+    if (lastChangeId !== refreshedToken.lastChangeId) {
+      store.dispatch('data/setGoogleToken', {
+        ...refreshedToken,
+        lastChangeId,
+      });
+    }
+  },
+  insertData(googleToken, data) {
+    return this.refreshToken(['https://www.googleapis.com/auth/drive.appdata'], googleToken)
+      .then(refreshedToken => saveFile(refreshedToken, data));
+  },
+  updateData(googleToken, data, appData) {
+    return this.refreshToken(['https://www.googleapis.com/auth/drive.appdata'], googleToken)
+      .then(refreshedToken => saveFile(refreshedToken, data, appData));
+  },
+};
diff --git a/src/services/syncSvc.js b/src/services/syncSvc.js
index 06a530d1..7f32651e 100644
--- a/src/services/syncSvc.js
+++ b/src/services/syncSvc.js
@@ -2,6 +2,96 @@ import localDbSvc from './localDbSvc';
 import store from '../store';
 import welcomeFile from '../data/welcomeFile.md';
 import utils from './utils';
+import userActivitySvc from './userActivitySvc';
+import googleHelper from './helpers/googleHelper';
+
+const lastSyncActivityKey = 'lastSyncActivity';
+let lastSyncActivity;
+const getStoredLastSyncActivity = () => parseInt(localStorage[lastSyncActivityKey], 10) || 0;
+const inactivityThreshold = 3 * 1000; // 3 sec
+const autoSyncAfter = 60 * 1000; // 1 min
+const isSyncAvailable = () => window.navigator.onLine !== false &&
+  !!store.getters['data/loginToken'];
+
+function isSyncWindow() {
+  const storedLastSyncActivity = getStoredLastSyncActivity();
+  return lastSyncActivity === storedLastSyncActivity ||
+    Date.now() > inactivityThreshold + storedLastSyncActivity;
+}
+
+function isAutoSyncNeeded() {
+  const storedLastSyncActivity = getStoredLastSyncActivity();
+  return Date.now() > autoSyncAfter + storedLastSyncActivity;
+}
+
+function setLastSyncActivity() {
+  const currentDate = Date.now();
+  lastSyncActivity = currentDate;
+  localStorage[lastSyncActivityKey] = currentDate;
+}
+
+function sync() {
+  const googleToken = store.getters['data/loginToken'];
+  return googleHelper.getChanges(googleToken)
+    .then((changes) => {
+      console.log(changes);
+      const localChanges = [];
+      [
+        store.state.files,
+      ].forEach((moduleState) => {
+        Object.keys(moduleState.itemMap).forEach((id) => {
+          localChanges.push(moduleState.itemMap[id]);
+        });
+      });
+      const uploadLocalChange = () => {
+        const localChange = localChanges.pop();
+        if (!localChange) {
+          return null;
+        }
+        return googleHelper.insertAppData(googleToken, localChange)
+          .then(() => uploadLocalChange());
+      };
+      return uploadLocalChange();
+    });
+}
+
+function requestSync() {
+  store.dispatch('queue/enqueueSyncRequest', () => new Promise((resolve, reject) => {
+    let intervalId;
+    const attempt = () => {
+      // Only start syncing when these conditions are met
+      if (userActivitySvc.isActive() && isSyncWindow()) {
+        clearInterval(intervalId);
+        if (!isSyncAvailable()) {
+          // Cancel sync
+          reject();
+        } else {
+          // Call setLastSyncActivity periodically
+          intervalId = utils.setInterval(() => setLastSyncActivity(), 1000);
+          setLastSyncActivity();
+          const cleaner = cb => (res) => {
+            clearInterval(intervalId);
+            cb(res);
+          };
+          sync().then(cleaner(resolve), cleaner(reject));
+        }
+      }
+    };
+    intervalId = utils.setInterval(() => attempt(), 1000);
+    attempt();
+  }));
+}
+
+// Sync periodically
+utils.setInterval(() => {
+  if (isSyncAvailable() &&
+    userActivitySvc.isActive() &&
+    isSyncWindow() &&
+    isAutoSyncNeeded()
+  ) {
+    requestSync();
+  }
+}, 1000);
 
 const ifNoId = cb => (obj) => {
   if (obj.id) {
@@ -12,33 +102,38 @@ const ifNoId = cb => (obj) => {
 
 // Load the DB on boot
 localDbSvc.sync()
-  // Watch file changing
+  // And watch file changing
   .then(() => store.watch(
     () => store.getters['files/current'].id,
     () => Promise.resolve(store.getters['files/current'])
-      // If current file has no ID, get the most recent file
-      .then(ifNoId(() => store.getters['files/mostRecent']))
-      // If still no ID, create a new file
-      .then(ifNoId(() => {
-        const contentId = utils.uid();
-        store.commit('contents/setItem', {
-          id: contentId,
-          text: welcomeFile,
-        });
-        const fileId = utils.uid();
-        store.commit('files/setItem', {
-          id: fileId,
-          name: 'Welcome file',
-          contentId,
-        });
-        return store.state.files.itemMap[fileId];
-      }))
-      .then((currentFile) => {
-        store.commit('files/setCurrentId', currentFile.id);
-        store.dispatch('files/patchCurrent', {}); // Update `updated` field to make it the mostRecent
-      }),
-    {
+    // If current file has no ID, get the most recent file
+    .then(ifNoId(() => store.getters['files/mostRecent']))
+    // If still no ID, create a new file
+    .then(ifNoId(() => {
+      const contentId = utils.uid();
+      store.commit('contents/setItem', {
+        id: contentId,
+        text: welcomeFile,
+      });
+      const fileId = utils.uid();
+      store.commit('files/setItem', {
+        id: fileId,
+        name: 'Welcome file',
+        contentId,
+      });
+      return store.state.files.itemMap[fileId];
+    }))
+    .then((currentFile) => {
+      store.commit('files/setCurrentId', currentFile.id);
+      store.dispatch('files/patchCurrent', {}); // Update `updated` field to make it the mostRecent
+    }), {
       immediate: true,
     }));
 
-utils.setInterval(() => localDbSvc.sync(), 1200);
+// Sync local DB periodically
+utils.setInterval(() => localDbSvc.sync(), 1000);
+
+export default {
+  isSyncAvailable,
+  requestSync,
+};
diff --git a/src/services/userActivitySvc.js b/src/services/userActivitySvc.js
new file mode 100644
index 00000000..a0715226
--- /dev/null
+++ b/src/services/userActivitySvc.js
@@ -0,0 +1,28 @@
+const inactiveAfter = 2 * 60 * 1000; // 2 minutes
+let lastActivity;
+let lastFocus;
+const lastFocusKey = 'lastWindowFocus';
+
+function setLastActivity() {
+  lastActivity = Date.now();
+}
+
+function setLastFocus() {
+  lastFocus = Date.now();
+  localStorage[lastFocusKey] = lastFocus;
+  setLastActivity();
+}
+
+setLastFocus();
+window.addEventListener('focus', setLastFocus);
+window.document.addEventListener('mousedown', setLastActivity);
+window.document.addEventListener('keydown', setLastActivity);
+
+export default {
+  isFocused() {
+    return parseInt(localStorage[lastFocusKey], 10) === lastFocus;
+  },
+  isActive() {
+    return lastActivity > Date.now() - inactiveAfter && this.isFocused();
+  },
+};
diff --git a/src/services/userSvc.js b/src/services/userSvc.js
deleted file mode 100644
index 8a5321eb..00000000
--- a/src/services/userSvc.js
+++ /dev/null
@@ -1,70 +0,0 @@
-import utils from './utils';
-import store from '../store';
-
-const googleClientId = '241271498917-t4t7d07qis7oc0ahaskbif3ft6tk63cd.apps.googleusercontent.com';
-const appUri = 'http://localhost:8080/';
-const googleAppsDomain = null;
-const origin = `${location.protocol}//${location.host}`;
-
-export default {
-  oauth2Context: null,
-  signinWithGoogle() {
-    this.cleanOauth2Context();
-    const state = utils.uid();
-    let authorizeUrl = 'https://accounts.google.com/o/oauth2/v2/auth';
-    authorizeUrl = utils.addQueryParam(authorizeUrl, 'client_id', googleClientId);
-    authorizeUrl = utils.addQueryParam(authorizeUrl, 'response_type', 'token');
-    authorizeUrl = utils.addQueryParam(authorizeUrl, 'redirect_uri', `${appUri}oauth2/callback.html`);
-    authorizeUrl = utils.addQueryParam(authorizeUrl, 'state', state);
-    if (googleAppsDomain) {
-      authorizeUrl = utils.addQueryParam(authorizeUrl, 'scope', 'openid email');
-      authorizeUrl = utils.addQueryParam(authorizeUrl, 'hd', googleAppsDomain);
-    } else {
-      authorizeUrl = utils.addQueryParam(authorizeUrl, 'scope', 'profile email');
-    }
-    const wnd = window.open(authorizeUrl);
-    if (!wnd) {
-      return Promise.resolve();
-    }
-    return new Promise((resolve) => {
-      const msgHandler = (event) => {
-        if (event.source === wnd
-          && event.origin === origin
-          && event.data
-          && event.data.state === state
-        ) {
-          this.cleanOauth2Context();
-          if (event.data.accessToken) {
-            store.dispatch('data/patchTokens', {
-              googleToken: {
-                accessToken: event.data.accessToken,
-              },
-            });
-            resolve();
-          }
-        }
-      };
-      window.addEventListener('message', msgHandler);
-      const checkClosedInterval = setInterval(() => {
-        if (this.oauth2Context && this.oauth2Context.wnd.closed) {
-          this.cleanOauth2Context();
-        }
-      }, 200);
-      this.oauth2Context = {
-        wnd,
-        msgHandler,
-        checkClosedInterval,
-      };
-    });
-  },
-  cleanOauth2Context() {
-    if (this.oauth2Context) {
-      clearInterval(this.oauth2Context.checkClosedInterval);
-      if (!this.oauth2Context.wnd.closed) {
-        this.oauth2Context.wnd.close();
-      }
-      window.removeEventListener('message', this.oauth2Context.msgHandler);
-      this.oauth2Context = null;
-    }
-  },
-};
diff --git a/src/services/utils.js b/src/services/utils.js
index 71c99d23..df41b5b7 100644
--- a/src/services/utils.js
+++ b/src/services/utils.js
@@ -1,20 +1,29 @@
+// For uid()
 const crypto = window.crypto || window.msCrypto;
 const alphabet = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
 const radix = alphabet.length;
 const array = new Uint32Array(20);
+
+// For addQueryParam()
 const urlParser = window.document.createElement('a');
 
+// For loadScript()
+const scriptLoadingPromises = Object.create(null);
+
+// For startOauth2()
+const origin = `${location.protocol}//${location.host}`;
+
 export default {
   uid() {
     crypto.getRandomValues(array);
     return array.cl_map(value => alphabet[value % radix]).join('');
   },
   setInterval(func, interval) {
-    const randomizedInterval = Math.floor((1 + ((Math.random() - 0.5) * 0.1)) * interval);
-    setInterval(() => func(), randomizedInterval);
+    const randomizedInterval = Math.floor((1 + (Math.random() * 0.1)) * interval);
+    return setInterval(() => func(), randomizedInterval);
   },
   addQueryParam(url, key, value) {
-    if (!url || !key || !value) {
+    if (!url || !key || value == null) {
       return url;
     }
     urlParser.href = url;
@@ -26,4 +35,191 @@ export default {
     urlParser.search += `${encodeURIComponent(key)}=${encodeURIComponent(value)}`;
     return urlParser.href;
   },
+  loadScript(url) {
+    if (!scriptLoadingPromises[url]) {
+      scriptLoadingPromises[url] = new Promise((resolve, reject) => {
+        const script = document.createElement('script');
+        script.onload = resolve;
+        script.onerror = () => {
+          scriptLoadingPromises[url] = null;
+          reject();
+        };
+        script.src = url;
+        document.head.appendChild(script);
+      });
+    }
+    return scriptLoadingPromises[url];
+  },
+  startOauth2(url, params = {}, silent = false) {
+    const oauth2Context = {};
+
+    // Build the authorize URL
+    const state = this.uid();
+    params.state = state;
+    params.redirect_uri = `${origin}/oauth2/callback.html`;
+    let authorizeUrl = url;
+    Object.keys(params).forEach((key) => {
+      authorizeUrl = this.addQueryParam(authorizeUrl, key, params[key]);
+    });
+    if (silent) {
+      // Use an iframe as wnd for silent mode
+      oauth2Context.iframeElt = document.createElement('iframe');
+      oauth2Context.iframeElt.style.position = 'absolute';
+      oauth2Context.iframeElt.style.left = '-9999px';
+      oauth2Context.iframeElt.onload = () => {
+        oauth2Context.closeTimeout = setTimeout(() => oauth2Context.clean(), 5 * 1000);
+      };
+      oauth2Context.iframeElt.src = authorizeUrl;
+      document.body.appendChild(oauth2Context.iframeElt);
+      oauth2Context.wnd = oauth2Context.iframeElt.contentWindow;
+    } else {
+      // Open a new tab otherwise
+      oauth2Context.wnd = window.open(authorizeUrl);
+      // If window opening has been blocked by the browser
+      if (!oauth2Context.wnd) {
+        return Promise.reject();
+      }
+      oauth2Context.closeTimeout = setTimeout(() => oauth2Context.clean(), 120 * 1000);
+    }
+    return new Promise((resolve, reject) => {
+      oauth2Context.clean = (errorMsg) => {
+        clearInterval(oauth2Context.checkClosedInterval);
+        if (!silent && !oauth2Context.wnd.closed) {
+          oauth2Context.wnd.close();
+        }
+        if (oauth2Context.iframeElt) {
+          document.body.removeChild(oauth2Context.iframeElt);
+        }
+        clearTimeout(oauth2Context.closeTimeout);
+        window.removeEventListener('message', oauth2Context.msgHandler);
+        oauth2Context.clean = () => {}; // Prevent from cleaning several times
+        if (errorMsg) {
+          reject(new Error(errorMsg));
+        }
+      };
+
+      oauth2Context.msgHandler = (event) => {
+        if (event.source === oauth2Context.wnd &&
+          event.origin === origin &&
+          event.data &&
+          event.data.state === state
+        ) {
+          oauth2Context.clean();
+          if (event.data.accessToken) {
+            resolve(event.data);
+          } else {
+            reject(event.data);
+          }
+        }
+      };
+      window.addEventListener('message', oauth2Context.msgHandler);
+
+      oauth2Context.checkClosedInterval = !silent && setInterval(() => {
+        if (oauth2Context.wnd.closed) {
+          oauth2Context.clean();
+        }
+      }, 200);
+    });
+  },
+  request(configParam) {
+    const timeout = 30 * 1000; // 30 sec
+    let retryAfter = 500; // 500 ms
+    const maxRetryAfter = 30 * 1000; // 30 sec
+    const config = Object.assign({}, configParam);
+    config.headers = Object.assign({
+      'Content-Type': 'application/json',
+    }, config.headers);
+
+    function parseHeaders(xhr) {
+      const pairs = xhr.getAllResponseHeaders().trim().split('\n');
+      return pairs.reduce((headers, header) => {
+        const split = header.trim().split(':');
+        const key = split.shift().trim().toLowerCase();
+        const value = split.join(':').trim();
+        headers[key] = value;
+        return headers;
+      }, {});
+    }
+
+    function isRetriable(err) {
+      switch (err.status) {
+        case 403:
+          {
+            const googleReason = ((((err.body || {}).error || {}).errors || [])[0] || {}).reason;
+            return googleReason === 'rateLimitExceeded' || googleReason === 'userRateLimitExceeded';
+          }
+        case 429:
+          return true;
+        default:
+          if (err.status >= 500 && err.status < 600) {
+            return true;
+          }
+      }
+      return false;
+    }
+
+    const attempt =
+      () => new Promise((resolve, reject) => {
+        const xhr = new window.XMLHttpRequest();
+        let timeoutId;
+
+        xhr.onload = () => {
+          clearTimeout(timeoutId);
+          const result = {
+            status: xhr.status,
+            headers: parseHeaders(xhr),
+            body: xhr.responseText,
+          };
+          try {
+            result.body = JSON.parse(result.body);
+          } catch (e) {
+            // ignore
+          }
+          if (result.status >= 200 && result.status < 300) {
+            resolve(result);
+            return;
+          }
+          reject(result);
+        };
+
+        xhr.onerror = () => {
+          clearTimeout(timeoutId);
+          reject(new Error('Network request failed.'));
+        };
+
+        timeoutId = setTimeout(() => {
+          xhr.abort();
+          reject(new Error('Network request timeout.'));
+        }, timeout);
+
+        // Add query params to URL
+        let url = config.url || '';
+        if (config.params) {
+          Object.keys(config.params).forEach((key) => {
+            url = this.addQueryParam(url, key, config.params[key]);
+          });
+        }
+
+        xhr.open(config.method, url);
+        Object.keys(config.headers).forEach((key) => {
+          xhr.setRequestHeader(key, config.headers[key]);
+        });
+        xhr.send(config.body ? JSON.stringify(config.body) : null);
+      })
+      .catch((err) => {
+        // Try again later in case of retriable error
+        if (isRetriable(err) && retryAfter < maxRetryAfter) {
+          return new Promise(
+              (resolve) => {
+                setTimeout(resolve, retryAfter);
+                // Exponential backoff
+                retryAfter *= 2;
+              })
+            .then(attempt);
+        }
+        throw err;
+      });
+
+    return attempt();
+  },
 };
diff --git a/src/store/index.js b/src/store/index.js
index bab4df2b..1b6f5352 100644
--- a/src/store/index.js
+++ b/src/store/index.js
@@ -9,6 +9,7 @@ import layout from './modules/layout';
 import editor from './modules/editor';
 import explorer from './modules/explorer';
 import modal from './modules/modal';
+import queue from './modules/queue';
 
 Vue.use(Vuex);
 
@@ -32,6 +33,7 @@ const store = new Vuex.Store({
     editor,
     explorer,
     modal,
+    queue,
   },
   strict: debug,
   plugins: debug ? [createLogger()] : [],
diff --git a/src/store/modules/data.js b/src/store/modules/data.js
index 44f87151..e4731daf 100644
--- a/src/store/modules/data.js
+++ b/src/store/modules/data.js
@@ -13,30 +13,42 @@ const module = moduleTemplate(empty);
 
 const getter = id => state => state.itemMap[id] || empty(id);
 
-const localSettingsToggler = propertyName => ({ getters, dispatch }, value) => {
-  dispatch('patchLocalSettings', {
-    [propertyName]: value === undefined ? !getters.localSettings[propertyName] : value,
-  });
-};
-
 module.getters = {
   ...module.getters,
   localSettings: getter('localSettings'),
+  settings: getter('settings'),
+  syncData: getter('syncData'),
   tokens: getter('tokens'),
+  googleTokens: (state, getters) => getters.tokens.google || {},
+  loginToken: (state, getters) => {
+    const googleTokens = getters.googleTokens;
+    // Return the first googleToken that has the isLogin flag
+    const loginSubs = Object.keys(googleTokens)
+      .filter(sub => googleTokens[sub].isLogin);
+    return googleTokens[loginSubs[0]];
+  },
 };
 
+const patcher = id => ({ getters, commit }, value) => commit('patchOrSetItem', {
+  ...value,
+  id,
+});
+
+const localSettingsToggler = propertyName => ({ getters, dispatch }, value) => dispatch('patchLocalSettings', {
+  [propertyName]: value === undefined ? !getters.localSettings[propertyName] : value,
+});
+
 module.actions = {
   ...module.actions,
-  patchLocalSettings({ getters, commit }, value) {
-    commit('patchOrSetItem', {
-      ...value,
-      id: 'localSettings',
-    });
-  },
-  patchTokens({ getters, commit }, value) {
-    commit('patchOrSetItem', {
-      ...value,
-      id: 'tokens',
+  patchLocalSettings: patcher('localSettings'),
+  patchSyncData: patcher('syncData'),
+  patchTokens: patcher('tokens'),
+  setGoogleToken({ getters, dispatch }, googleToken) {
+    dispatch('patchTokens', {
+      google: {
+        ...getters.googleTokens,
+        [googleToken.sub]: googleToken,
+      },
     });
   },
   toggleNavigationBar: localSettingsToggler('showNavigationBar'),
diff --git a/src/store/modules/queue.js b/src/store/modules/queue.js
new file mode 100644
index 00000000..97d66bf3
--- /dev/null
+++ b/src/store/modules/queue.js
@@ -0,0 +1,42 @@
+const setter = propertyName => (state, value) => {
+  state[propertyName] = value;
+};
+
+let queue = Promise.resolve();
+
+export default {
+  namespaced: true,
+  state: {
+    isEmpty: true,
+    isSyncRequested: false,
+  },
+  mutations: {
+    setIsEmpty: setter('isEmpty'),
+    setIsSyncRequested: setter('isSyncRequested'),
+  },
+  actions: {
+    enqueue({ state, commit }, cb) {
+      if (state.isEmpty) {
+        commit('setIsEmpty', false);
+      }
+      const newQueue = queue
+        .then(cb)
+        .catch((err) => {
+          console.error(err);
+        })
+        .then(() => {
+          if (newQueue === queue) {
+            commit('setIsEmpty', true);
+          }
+        });
+      queue = newQueue;
+    },
+    enqueueSyncRequest({ state, commit, dispatch }, cb) {
+      if (!state.isSyncRequested) {
+        commit('setIsSyncRequested', true);
+        const unset = () => commit('setIsSyncRequested', false);
+        dispatch('enqueue', () => cb().then(unset, unset));
+      }
+    },
+  },
+};
diff --git a/static/oauth2/callback.html b/static/oauth2/callback.html
index 17c3059a..6501a287 100644
--- a/static/oauth2/callback.html
+++ b/static/oauth2/callback.html
@@ -4,6 +4,7 @@
     <script>
       var state;
       var accessToken;
+      var expiresIn;
       function parse(search) {
         (search || '').slice(1).split('&').forEach(function (param) {
           var split = param.split('=');
@@ -13,15 +14,18 @@
             state = value;
           } else if (key === 'access_token') {
             accessToken = value;
+          } else if (key === 'expires_in') {
+            expiresIn = value;
           }
         });
       }
       parse(location.search);
       parse(location.hash);
       var origin = location.protocol + '//' + location.host;
-      opener.postMessage({
+      (window.opener || window.parent).postMessage({
         state: state,
-        accessToken: accessToken
+        accessToken: accessToken,
+        expiresIn: expiresIn
       }, origin);
     </script>
   </body>