# File activemodel/lib/active_model/secure_password.rb, line 53
def has_secure_password(options = {})
  # Load bcrypt gem only when has_secure_password is used.
  # This is to avoid ActiveModel (and by extension the entire framework)
  # being dependent on a binary library.
  begin
    require 'bcrypt'
  rescue LoadError
    $stderr.puts "You don't have bcrypt installed in your application. Please add it to your Gemfile and run bundle install"
    raise
  end

  include InstanceMethodsOnActivation

  if options.fetch(:validations, true)
    include ActiveModel::Validations

    # This ensures the model has a password by checking whether the password_digest
    # is present, so that this works with both new and existing records. However,
    # when there is an error, the message is added to the password attribute instead
    # so that the error message will make sense to the end-user.
    validate do |record|
      record.errors.add(:password, :blank) unless record.password_digest.present?
    end

    validates_length_of :password, maximum: ActiveModel::SecurePassword::MAX_PASSWORD_LENGTH_ALLOWED
    validates_confirmation_of :password, allow_blank: true
  end

  # This code is necessary as long as the protected_attributes gem is supported.
  if respond_to?(:attributes_protected_by_default)
    def self.attributes_protected_by_default #:nodoc:
      super + ['password_digest']
    end
  end
end

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

The following validations are added automatically:

• Password must be present on creation

• Password length should be less than or equal to 72 characters

• Confirmation of password (using a password_confirmation attribute)

If password confirmation validation is not needed, simply leave out the value for password_confirmation (i.e. don't provide a form field for it). When this attribute has a nil value, the validation will not be triggered.

For further customizability, it is possible to supress the default validations by passing validations: false as an argument.

Add bcrypt (~> 3.1.7) to Gemfile to use has_secure_password:

gem 'bcrypt', '~> 3.1.7'

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')      # => false
User.find_by(name: 'david').try(:authenticate, 'mUc3m00RsqyRe') # => user