Example user with a BCrypt password

user.rb

require 'bcrypt'

  class User
    include DataMapper::Resource

    attr_accessor :password, :password_confirmation, :password_reset

    timestamps :at

    property :id,           Serial
    property :username,     String,   :length => 4..30, :unique => true, :required => true
    property :crypted_pass, String,   :length => 60..60, :required => true, :writer => :protected
    property :email,        String,   :length => 5..200, :required => true,
                                      :format => :email_address

    validates_presence_of :password, :password_confirmation, :if => :password_required?
    validates_confirmation_of :password, :if => :password_required?

    before :valid?, :crypt_password

    def password_required?
      new? or password_reset
    end

    def reset_password(password, confirmation)
      update(:password_reset => true, :password => password, :password_confirmation => confirmation)
    end

    # Hash the password using BCrypt
    #
    # BCrypt is a lot more secure than a hash made for speed such as the SHA algorithm. BCrypt also
    # takes care of adding a salt before hashing.  The whole thing is encoded in a string 60 bytes long.
    def crypt_password
      self.crypted_pass = BCrypt::Password.create(password) if password
    end

    # Prepare a BCrypt hash from the stored password, overriding the default reader
    #
    # return the `:no_password` symbol if the property has no content.  This is for
    # the safety of the authenticate method.  It's easy to pass a nil password to 
    # that method, but passing a specific symbol takes effort.
    def crypted_pass
      pass = super
      if pass
         BCrypt::Password.new(pass)
      else
        :no_password
      end
    end

    def authenticate(password)
      crypted_pass == password
    end

    def self.authenticate(username, password)
      un = username.to_s.downcase
      u = first(:conditions => ['lower(email) = ? OR lower(username) = ?', un, un])
      if u && u.authenticate(password)
        u
      else
        nil
      end
    end
  end