Add user auth

[happypeter]

This time rails3.1 gives us has_secure_password, things get much sweeter!

http://railscasts.com/episodes/250-authentication-from-scratch-revised?autoplay=true

[happypeter]

注意使用 has_secure_password 的时候要注意数据库里是否有 password_digest, 另外就是 form 中 password_comfirmation 的提交 id 的名字也要标准， 不然密码匹配检测不会运行。

[happypeter]

-    <%= label_tag :passward %><br />
-    <%= password_field_tag :passward %>
+    <%= label_tag :password %><br />
+    <%= password_field_tag :password %>

if you have passward in your login form, you won't get a error, well, when you submit the form, you see

 "passward"=>"111111",

when it should be

 "password"=>"[filtered]",