a starting point for authentication with mongomapper and rails

authentication.rb

# include this in application controller
module Authentication
  protected
    # Inclusion hook to make #current_user and #signed_in?
    # available as ActionView helper methods.
    def self.included(base)
      base.send :helper_method, :current_user, :signed_in?, :authorized? if base.respond_to? :helper_method
    end
    
    # Returns true or false if the user is signed in.
    # Preloads @current_user with the user model if they're signed in.
    def signed_in?
      !!current_user
    end
    
    # Accesses the current user from the session.
    # Future calls avoid the database because nil is not equal to false.
    def current_user
      @current_user ||= (sign_in_from_session || sign_in_from_basic_auth) unless @current_user == false
    end
    
    # Store the given user id in the session.
    def current_user=(new_user)
      session[:user_id] = new_user ? new_user.id : nil
      @current_user = new_user || false
    end

    # Check if the user is authorized
    #
    # Override this method in your controllers if you want to restrict access
    # to only a few actions or if you want to check if the user
    # has the correct rights.
    #
    # Example:
    #
    #  # only allow nonbobs
    #  def authorized?
    #    current_user.name != "bob"
    #  end
    #
    def authorized?(action=nil, resource=nil, *args)
      signed_in?
    end

    # Filter method to enforce a sign_in requirement.
    #
    # To require sign_ins for all actions, use this in your controllers:
    #
    #   before_filter :sign_in_required
    #
    # To require sign_ins for specific actions, use this in your controllers:
    #
    #   before_filter :sign_in_required, :only => [ :edit, :update ]
    #
    # To skip this in a subclassed controller:
    #
    #   skip_before_filter :sign_in_required
    #
    def authenticate
      authorized? || access_denied
    end

    # Redirect as appropriate when an access request fails.
    #
    # The default action is to redirect to the sign_in screen.
    #
    # Override this method in your controllers if you want to have special
    # behavior in case the user is not authorized
    # to access the requested action.  For example, a popup window might
    # simply close itself.
    def access_denied
      respond_to do |format|
        format.html do
          store_location
          redirect_to new_session_path
        end
        # format.any doesn't work in rails version < http://dev.rubyonrails.org/changeset/8987
        # you may want to change format.any to e.g. format.any(:js, :xml)
        format.any do
          request_http_basic_authentication 'Web Password'
        end
      end
    end

    # Store the URI of the current request in the session.
    #
    # We can return to this location by calling #redirect_back_or_default.
    def store_location
      session[:return_to] = request.request_uri
    end

    # Redirect to the URI stored by the most recent store_location call or
    # to the passed default.  Set an appropriately modified
    #   after_filter :store_location, :only => [:index, :new, :show, :edit]
    # for any controller you want to be bounce-backable.
    def redirect_back_or_default(default)
      redirect_to(session[:return_to] || default)
      session[:return_to] = nil
    end
    
    # Called from #current_user.  First attempt to sign_in by the user id stored in the session.
    def sign_in_from_session
      if session[:user_id]
        self.current_user = User.find_by_id(session[:user_id])
      end
    end

    # Called from #current_user.  Now, attempt to sign_in by basic authentication information.
    def sign_in_from_basic_auth
      authenticate_with_http_basic do |email, password|
        self.current_user = User.authenticate(email, password)
      end
    end
    
    # This is ususally what you want; resetting the session willy-nilly wreaks
    # havoc with forgery protection, and is only strictly necessary on sign_in.
    # However, **all session state variables should be unset here**.
    def sign_out_keeping_session!
      # Kill server-side auth cookie
      @current_user = false     # not signed in, and don't do it for me
      session[:user_id] = nil   # keeps the session but kill our variable
      # explicitly kill any other session variables you set
    end

    # The session should only be reset at the tail end of a form POST --
    # otherwise the request forgery protection fails. It's only really necessary
    # when you cross quarantine (signed-out to signed-in).
    def sign_out_killing_session!
      sign_out_keeping_session!
      reset_session
    end
end

factories.rb

# factory girl factories
Factory.define(:user) do |u|
  u.sequence(:email) { |n| "john#{n}@doe.com" }
  u.password "testing"
  u.password_confirmation "testing"
end

new_user_and_new_session.html.erb

<%- form_for @user do |form| -%>
  <%= form.error_messages %>
  <ul>
    <li>
      <%= form.label :email %>
      <%= form.text_field :email %>
    </li>
    <li>
      <%= form.label :password %>
      <%= form.password_field :password %>
    </li>
    <li>
      <%= form.label :password_confirmation, 'Confirm Password' %>
      <%= form.password_field :password_confirmation %>
    </li>
    <li class="submit">
      <%= submit_tag 'Sign Up', :disable_with => 'Signing you up...' %>
      or <%= link_to 'sign in', new_session_path %>
    </li>
  </ul>
<%- end -%>

<%- form_tag session_path do -%>
  <ul>
    <li>
      <%= label_tag 'email', 'Email' %>
      <%= text_field_tag :email %>
    </li>
    <li>
      <%= label_tag 'password', 'Password' %>
      <%= password_field_tag :password %>
    </li>
    <li class="submit">
      <%= submit_tag 'Sign In', :disable_with => 'Signing you in...' %>
      or <%= link_to 'sign up', new_user_path %>
    </li>
  </ul>
<%- end -%>

sessions_controller.rb

class UsersController < ApplicationController
  def new
    @user = User.new
    render :layout => 'sessions'
  end
  
  def create
    @user = User.new(params[:user])
    if @user.save
      self.current_user = @user
      redirect_to root_path
    else
      render 'new', :layout => 'sessions'
    end
  end
end

test_helper.rb

class ActiveSupport::TestCase
  # clear each collection in setup
  def setup
    Dir[Rails.root + 'app/models/**/*.rb'].each do |model_path|
      model_name = File.basename(model_path).gsub(/\.rb$/, '')
      klass = model_name.classify.constantize
      klass.collection.clear
    end
  end
  # stuff removed for brevity
end

user.rb

# uses bcrypt-ruby gem for password hashing be sure to config.gem it
require 'digest/sha1'
class User
  include MongoMapper::Document
  
  key :email, String, :required => true
  key :crypted_password, String
  key :reset_password_code, String
  key :reset_password_code_until, Time
  
  RegEmailName   = '[\w\.%\+\-]+'
  RegDomainHead  = '(?:[A-Z0-9\-]+\.)+'
  RegDomainTLD   = '(?:[A-Z]{2}|com|org|net|gov|mil|biz|info|mobi|name|aero|jobs|museum)'
  RegEmailOk     = /\A#{RegEmailName}@#{RegDomainHead}#{RegDomainTLD}\z/i
  
  def self.authenticate(email, secret)
    u = User.first(:conditions => {:email => email.downcase})
    u && u.authenticated?(secret) ? u : nil
  end
  
  validates_length_of :email, :within => 6..100, :allow_blank => true
  validates_format_of :email, :with => RegEmailOk, :allow_blank => true
  
  PasswordRequired = Proc.new { |u| u.password_required? }
  validates_presence_of :password, :if => PasswordRequired
  validates_confirmation_of :password, :if => PasswordRequired, :allow_nil => true
  validates_length_of :password, :minimum => 6, :if => PasswordRequired, :allow_nil => true
  
  def authenticated?(secret)
    password == secret ? true : false
  end
  
  def password
    if crypted_password.present?
      @password ||= BCrypt::Password.new(crypted_password)
    else
      nil
    end
  end
  
  def password=(value)
    if value.present?
      @password = value
      self.crypted_password = BCrypt::Password.create(value)
    end
  end
  
  def email=(new_email)
    new_email.downcase! unless new_email.nil?
    write_attribute(:email, new_email)
  end
  
  def password_required?
    crypted_password.blank? || !password.blank?
  end
  
  def set_password_code!
    seed = "#{email}#{Time.now.to_s.split(//).sort_by {rand}.join}"
    self.reset_password_code_until = 1.day.from_now
    self.reset_password_code = Digest::SHA1.hexdigest(seed)
    save!
  end
end

user_controller_test.rb

require 'test_helper'

class SessionsControllerTest < ActionController::TestCase
  context "Visiting the sign in form" do
    setup { get :new }
    should_respond_with :success
    should "display signup form" do
      assert_select 'form[action=?]', session_path do
        assert_select 'input[id=?]', 'email'
        assert_select 'input[id=?]', 'password'
      end
    end
  end
  
  context "Submitting the sign in form with good credentials" do
    setup do
      @user = Factory(:user)
      post :create, :email => @user.email, :password => 'testing'
    end
    should_be_signed_in_as { @user }
    should_redirect_to_root
  end
  
  context "Submitting the sign in form with bad credentials" do
    setup do
      @user = Factory(:user)
      post :create, :email => @user.email, :password => 'FAIL'
    end
    
    should_not_be_signed_in
    should_redirect_to('sign in') { new_session_path }
  end
  
  context "Logging out" do
    setup do
      sign_in_as 'john@doe.com'
      delete :destroy
    end
    
    should_not_be_signed_in
    should_respond_with :success
  end
end

user_test.rb

require 'test_helper'

class UserTest < ActiveSupport::TestCase
  should "validate presence of email" do
    user = User.new
    user.should have_error_on(:email)
    user.email = 'foo@bar.com'
    user.should_not have_error_on(:email)
  end
  
  should "validate length of email" do
    user = User.new
    user.email = 'a@a'
    user.should have_error_on(:email)
    user.email = 'r@a.wk'
  end
  
  should "always store email as lower case" do
    user = User.new
    user.email = 'F@FOOBAR.COM'
    user.email.should == 'f@foobar.com'
  end
  
  should "be able to set user's reset password code" do
    user = Factory(:user)
    user.reset_password_code.should be_nil
    user.reset_password_code_until.should be_nil
    user.set_password_code!
    user.reset_password_code.should_not be_nil
    user.reset_password_code_until.should_not be_nil
  end
  
  context "Authentication" do    
    should 'work with existing email and correct password' do
      user = Factory(:user)
      User.authenticate(user.email, 'testing').should == user
    end
    
    should 'work with existing email (case insensitive) and password' do
      user = Factory(:user)
      User.authenticate(user.email.upcase, 'testing').should == user
    end
    
    should 'not work with existing email and incorrect password' do
      User.authenticate('john@doe.com', 'foobar').should be_nil
    end
    
    should 'not work with non-existant email' do
      User.authenticate('foo@bar.com', 'foobar').should be_nil
    end
  end
  
  context "password" do
    should 'be required if crypted password is blank' do
      User.new.should have_error_on(:password)
    end
    
    should 'not be required if crypted password is present' do
      user = User.new
      user.crypted_password = BCrypt::Password.create('foobar')
      user.should_not have_error_on(:password)
    end
    
    should "validate the length of password" do
      user = User.new
      user.password = '1234'
      user.should have_error_on(:password)
      user.password = '123456'
      user.should_not have_error_on(:password)
    end
  end
end

users_controller_test.rb

require 'test_helper'

class UsersControllerTest < ActionController::TestCase
  context "Visiting the signup form" do
    setup { get :new }
    should_respond_with :success
  end
  
  context "Attempting to signup with valid information" do
    setup { post :create, :user => Factory.attributes_for(:user) }
    should_change 'User.count', :by => 1
    
    should "sign user in" do
      session[:user_id].should == assigns(:user).id
    end
    
    should_redirect_to('home page') { root_path }
  end
  
  context "Attempting to signup with invalid information" do
    setup { post :create, :user => {}}
    should_not_change 'User.count'
    should_not_be_signed_in
    should_render_template :new
  end
end

Hey @jnunemaker, thanks for sharing the code! There is one mistake tho: UsersController is defined in file called sessions_controller.rb and there doesn't seem to be file with SessionsController. Also, SessionsControllerTest is defined in file called user_controller_test.rb.