module ActiveModel::SecurePassword::ClassMethods

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

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

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

gem 'bcrypt', '~> 3.1.7'

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

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

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

* Confirmation of password (using a +password_confirmation+ attribute)
* Password length should be less than or equal to 72 characters
* Password must be present on creation
The following validations are added automatically:

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

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
end