Devise: Password complexity

application_service.rb

# app/services/application_service.rb

class ApplicationService
  def self.call(*args, &block)
    new(*args, &block).call
  end
end

check_password_complexity_service.rb

# app/services/check_password_complexity_service.rb

class CheckPasswordComplexityService < ApplicationService
  attr_reader :password, :required_complexity

  def initialize(password, required_complexity = 4)
    @password = password
    @required_complexity = required_complexity
  end

  def call
    score = uppercase_letters? + digits? + extra_chars? + downcase_letters?
    score >= required_complexity
  end

  private

  def digits?
    @password.match(/\d/) ? 1 : 0
  end

  def downcase_letters?
    @password.match(/[a-z]{1}/) ? 1 : 0
  end

  def extra_chars?
    @password.match(/[\W_]/) ? 1 : 0
  end

  def uppercase_letters?
    @password.match(/[A-Z]/) ? 1 : 0
  end
end

en.yml

# config/locales/en.yml

en:
  activerecord:
    errors:
      messages:
        complexity: 'complexity requirement not met. Please use: 1 uppercase, 1 lowercase, 1 digit and 1 special character'

user.rb

# app/models/user.rb

class User < ActiveRecord::Base
  devise :confirmable,
         :database_authenticatable,
         :recoverable,
         :registerable,
         :rememberable,
         :trackable,
         :validatable

  validate :password_complexity

  private

  def password_complexity
    return if password.nil?

    errors.add :password, :complexity unless CheckPasswordComplexityService.call(password)
  end
end

user_spec.rb

# spec/models/user_spec.rb

require 'rails_helper'

RSpec.describe User, type: :model do
  describe 'validations' do
    it { should validate_presence_of(:email) }
    it { should validate_length_of(:password).is_at_least(8) }
  end

  describe 'password_complexity' do
    context 'valid' do
      ['`', '~', '!', '@', '#', '$', '%', '^', '&', '*', '(', ')',
       '-', '_', '=', '+', '[', ']', '{', '}', '\\', '|', ';', ':',
       "'", '"', ',', '.', '<', '>', '/', '?'].each do |extra_char|
        it { should allow_value("Password12#{extra_char}").for(:password) }
      end
    end

    context 'invalid' do
      %w(12345678 password =+[]{}\| PASSWORD password1 pa$$word Password1 password_1).each do |password|
        it { should_not allow_value(password).for(:password) }
      end
    end
  end
end