Adds methods to set and authenticate against a BCrypt password. This mechanism requires you to have a password_digest attribute.

Validations for presence of password, confirmation of password (using a "password_confirmation" attribute) are automatically added. You can add more validations by hand if need be.

Example using Active Record (which automatically includes ActiveModel::SecurePassword):

  # Schema: User(name:string, password_digest:string)
  class User < ActiveRecord::Base
    has_secure_password
  end

  user = User.new(:name => "david", :password => "", :password_confirmation => "nomatch")
  user.save                                                      # => false, password required
  user.password = "mUc3m00RsqyRe"
  user.save                                                      # => false, confirmation doesn't match
  user.password_confirmation = "mUc3m00RsqyRe"
  user.save                                                      # => true
  user.authenticate("notright")                                  # => false
  user.authenticate("mUc3m00RsqyRe")                             # => user
  User.find_by_name("david").try(:authenticate, "notright")      # => nil
  User.find_by_name("david").try(:authenticate, "mUc3m00RsqyRe") # => user