diff --git a/src/js/account.js b/src/js/account.js
new file mode 100644
index 0000000..d8ddd0d
--- /dev/null
+++ b/src/js/account.js
@@ -0,0 +1,75 @@
+/**
+ * Create a user.
+ * @param {Object} user
+ *   properties: id, name, accessToken, expires, accessTokenSecret, albumId
+ */
+var User = function(user) {
+  for (var prop in user) {
+    this[prop] = user[prop];
+  }
+};
+
+var Account = {
+
+  getUsers: function(siteId) {
+    var users = localStorage.getItem(siteId + '_userInfo');
+    if (users) {
+      users = JSON.parse(users);
+      for (var id in users) {
+        // Remove expired user.
+        if (Account.isExpires(users[id])) {
+          delete users[id];
+        }
+      }
+      localStorage.setItem(siteId + '_userInfo', JSON.stringify(users));
+      return users;
+    }
+    return {};
+  },
+
+  getUser: function(siteId, userId) {
+    var users = Account.getUsers(siteId);
+    var user = users[userId];
+    if (user && Account.isExpires(user)) {
+      Account.removeUser(siteId, userId);
+      return null;
+    } else {
+      return user;
+    }
+  },
+
+  addUser: function(siteId, user) {
+    var users = Account.getUsers(siteId);
+    var userId = user.id;
+    if (!users[userId]) {
+      users[userId] = user;
+      users = JSON.stringify(users);
+      localStorage.setItem(siteId + '_userInfo', users);
+    }
+  },
+
+  updateUser: function(siteId, user) {
+    var users = Account.getUsers(siteId);
+    var userId = user.id;
+    if (users && users[userId]) {
+      users[userId] = user;
+      users = JSON.stringify(users);
+      localStorage.setItem(siteId + '_userInfo', users);
+    }
+  },
+  
+  removeUser: function(siteId, userId) {
+    var users = Account.getUsers(siteId);
+    delete users[userId];
+    users = JSON.stringify(users);
+    localStorage.setItem(siteId + '_userInfo', users);
+  },
+
+  isExpires: function(user) {
+    var expires = user.expires;
+    if (expires) {
+      return new Date().getTime() >= expires;
+    }
+    return false;
+  }
+};
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