http://techspeak.plainlystated.com/2010/03/drop-dead-simple-authentication-for.html

easy_auth.rb

require 'bcrypt'

module EasyAuth
  # http://techspeak.plainlystated.com/2010/03/drop-dead-simple-authentication-for.html

  # To generate a crypted password (in irb):
  # require 'easy_auth'
  # EasyAuth.encrypt_password('my_password')   # Put returned array in AUTHORIZED_USERS

  AUTHORIZED_USERS = {
    'username' => ["encrypted_password", "salt"]
  }

  SALT_CHARS = ['.', '/', '0'..'9', 'A'..'Z', 'a'..'z'].collect do |set|
    set.to_a
  end.flatten

  def self.encrypt_password(password, salt = nil)
    if salt.nil?
      salt = generate_salt
    end
    old_pass = password
    password = BCrypt::Password.create(salt + password).to_s
    [password, salt]
  end

  def self.generate_salt(length = 5)
    salt = ""
    length.times { salt << SALT_CHARS[rand(SALT_CHARS.length)] }
    salt
  end

  def auth_key(username)
    "#{_crypted_password(username)}::#{request.env['REMOTE_ADDR']}::#{request.env['HTTP_USER_AGENT']}"
  end

  def encrypt_password(username, password)
    salt = _salt(username)
    EasyAuth.encrypt_password(password, salt)[0]
  end

  def if_auth(username = request.cookies["username"], password = nil)
    if AUTHORIZED_USERS.has_key?(username)
      raise ArgumentError, "AUTHORIZED_USERS[#{username}] seems to have an invalid format. It should be the output of EasyAuth.encrypt_password('my_pass')" unless AUTHORIZED_USERS[username].size == 2

      if password.nil?
        authorized = valid_key?(username, request.cookies["key"])
      else
        if valid_password?(username, password)
          authorized = true

          crypted_key = encrypt_password(username, auth_key(username))
          response.set_cookie("username", username)
          response.set_cookie("key", crypted_key)
        end
      end

      if authorized
        return yield
      end
    end

    @error = "Login failed"
    erb :'/admin/login'
  end

  def valid_key?(username, key)
    BCrypt::Password.new(key) == _salt(username) + auth_key(username)
  end

  def valid_password?(username, password)
    BCrypt::Password.new(_crypted_password(username)) == _salt(username) + password
  end

  def _salt(username)
    AUTHORIZED_USERS.fetch(username, []).last
  end

  def _crypted_password(username)
    AUTHORIZED_USERS.fetch(username, []).first
  end
end