rails generate devise_views

rails generate migration add_username_to_users username:string

rake db:migrate

rails c

# projects_controller.rb

before_filter :authenticate_user!, :except => [:show, :index]

# routes.rb

devise_for :users, :path_names => { :sign_up => "register" }
# config/initializers/devise.rb

config.authentication_keys = [ :username ]

config.password_length = 4..20

<!— devise/sessions/new.html.erb —>

<% title "Sign in" %>

<%= form_for(resource_name, resource, :url => session_path(resource_name)) do |f| %>

  <p><%= f.label :username %><br />
<%= f.text_field :username %></p>
<p><%= f.label :password %><br />
<%= f.password_field :password %></p>
<!— … —>
<% end %>