title: Can't mass-assign protected attributes in Rails 3.2.3
body: <p>Migration </p>
  
  <pre><code>class CreateUsers &lt; ActiveRecord::Migration
    def change
      create_table :users do |t|
        t.string :name
        t.string :password_digest
  
        t.timestamps
      end
    end
  end
  </code></pre>
  
  <p>Model</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    attr_accessible :name, :password_digest
    validates :name, :presence =&gt; true, :uniqueness =&gt; true
    has_secure_password
  end
  </code></pre>
  
  <p>User's registration _form</p>
  
  <pre><code>.main_form
    = form_for @user do |f|
  
      %div
        = f.label :name
        = f.text_field :name, :size=&gt;40
  
      %div
        = f.label :password, "Password"
        = f.password_field :password
  
      %div
        = f.label :password_confirmation, "Confirmation"
        = f.password_field :password_field
  
      %div
        = f.submit 'Create user'
  </code></pre>
  
  <p>When I try to register a new user it throws an exception</p>
  
  <pre><code>ActiveModel::MassAssignmentSecurity::Error in UsersController#create
  
  Can't mass-assign protected attributes: password, password_field
  </code></pre>
  
  <p>What did I do wrong?</p>