Display login button in read-only mode.

IPython/frontend/html/notebook/static/js/loginwidget.js

@@ -22,12 +22,16 b' var IPython = (function (IPython) {'
 
     LoginWidget.prototype.style = function () {
         this.element.find('button#logout').button();
+        this.element.find('button#login').button();
     };
     LoginWidget.prototype.bind_events = function () {
         var that = this;
         this.element.find("button#logout").click(function () {
             window.location = "/logout";
         });
+        this.element.find("button#login").click(function () {
+            window.location = "/login";
+        });
     };
 
     // Set module variables

IPython/frontend/html/notebook/templates/layout.html

@@ -25,6 +25,8 b''
     <span id="login_widget">
       {% if current_user and current_user != 'anonymous' %}
         <button id="logout">Logout</button>
+      {% else %}
+        <button id="login">Login</button>
       {% end %}
     </span>
     {% block header %}

IPython/frontend/html/notebook/templates/notebook.html

@@ -54,6 +54,8 b''
       {% comment  when appropriate until notebook.html is templated %}
       {% if current_user and current_user != 'anonymous' %}
         <button id="logout">Logout</button>
+      {% else %}
+        <button id="login">Login</button>
       {% end %}
     </span>