Devise for user management and authentication.

Below is the details of the Devise Gem.
https://github.com/plataformatec/devise

The main purpose of this tutorial is to implement the devise gem and authenticate a user by user id and email.
Let's come to the implementation.

Step1.First, add devise gem in Gemfile.

gem 'devise', '3.4.1'

Step2.then after installing the gem

bundle install

Step3.Model and View Settings

$ rails generate devise:install
$ rails generate devise MODEL
$ rails generate devise:views

(if you want to change the layout of your views)

Step4.Run the migration.

rake db:migrate

Step5.config/environments/development.rb:

config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }

Step6.Other configuration settings
in /config/application.rb

config.action_mailer.delivery_method = :smtp
    ActionMailer::Base.smtp_settings = {
    address: "smtp.gmail.com",
    enable_starttls_auto: true,
    port: 587,
    authentication: :plain,
    user_name: ENV["MAIL_USERNAME"],
    password: ENV["MAIL_PASSWORD"],
    openssl_verify_mode: 'none'
    }

for environment settings please check the below article.
http://qiita.com/alokrawat050/items/0d7791b3915579f95791

Step7.Settings, user login by email or user_id
in your /model/user.rb

devise :database_authenticatable, :registerable,:confirmable, :lockable, :timeoutable,:recoverable, :rememberable, :trackable, :validatable, :authentication_keys => [:login]

here we are using :authentication_keys => [:login], to authenticate user's login.

and also add below code in /model/user.rb.
'# Virtual attribute for authenticating by either user_id or email

This is in addition to a real persisted field like 'user_id'

attr_accessor :login

  def login=(login)
    @login = login
  end

  def login
    @login || self.user_id || self.email
  end
  
  def self.find_for_database_authentication(warden_conditions)
    conditions = warden_conditions.dup
    if login = conditions.delete(:login)
      where(conditions.to_h).where(["user_id = :value OR email = :value", { :value => login.downcase }]).first
    else
      where(conditions.to_h).first
    end
  end

def send_devise_notification(notification, *args)
    devise_mailer.send(notification, self, *args).deliver_later
  end

Step8.Add below lline in /config/initializers/devise.rb file
line number 33 → config.authentication_keys = [:login ]

Step9.Changes in views
in /views/devise/sessions/new.html.erb

replace below code:

<%= f.label :email %>
<%= f.email_field :email, autofocus: true %>
↓
<%= f.label :login %>
<%= f.text_field :login, autofocus: true, class: 'form-control'  %>

in /views/devise/registrations/new.html.erb

<%= f.label :user_id %>
<%= f.text_field :user_id, class: 'form-control' %>

Then run your application.
If you have doubts then please feel free to ask.

Enjoy Coding.

Thanks & Best Regards,
Alok Rawat