devise with scrypt || bcrypt hack

devise_with_scrypt_or_bcrypt.rb

begin
  require 'devise'
  require 'devise/models/database_authenticatable'

  begin
    require 'bcrypt'
  rescue LoadError
  end

  begin
    require 'scrypt'
  rescue LoadError
  end

  module Devise

    def self.bcrypt(klass, password)
      ::BCrypt::Password.create("#{password}#{klass.pepper}", cost: klass.stretches).to_s
    end if defined? BCrypt

    def self.scrypt(klass, password)
      ::SCrypt::Password.create("#{password}#{klass.pepper}").to_s
    end if defined? SCrypt

    module Models
      # Verifies whether an password (ie from sign in) is the user password.
      def valid_password?(password)
        return false if encrypted_password.blank?
        if defined? SCrypt
          scrypt = ::SCrypt::Password.new(encrypted_password)
          password = ::SCrypt::Engine.hash_secret("#{password}#{self.class.pepper}", scrypt.cost + scrypt.salt)
        elsif defined? BCrypt
          bcrypt = ::BCrypt::Password.new(encrypted_password)
          password = ::BCrypt::Engine.hash_secret("#{password}#{self.class.pepper}", bcrypt.salt)
        else
          fail 'Missing one of scrypt or bcrypt-ruby'
        end
        Devise.secure_compare(password, encrypted_password)
      end

      def authenticatable_salt
        unless encrypted_password.blank?
          if defined? SCrypt
            password = ::SCrypt::Password.new(encrypted_password)
            password.cost + password.salt
          elsif defined? BCrypt
            ::BCrypt::Password.new(encrypted_password).salt
          else
            encrypted_password[0,29]
          end
        end
      end

    protected
      # Digests the password using bcrypt. Custom encryption should override
      # this method to apply their own algorithm.
      #
      # See https://github.com/plataformatec/devise-encryptable for examples
      # of other encryption engines.
      def password_digest(password)
        if defined? SCrypt
          Devise.scrypt(self.class, password)
        elsif defined? BCrypt
          Devise.bcrypt(self.class, password)
        else
          fail 'Missing scrypt or bcrypt gem for devise'
        end
      end
    end
  end
rescue LoadError
end