Rails 6.x+ Auth with MagicLinks using Rails Signed GlobalIDs

Password-less Authentication

Passwordless Authentication is very convenient for users and generally as secure as passwords (a good security authentication discussion can be found at: ).

A good approach is to make a short-lived link, and then transfer the security to a session.

I found that there seems to be three simple approaches:

  1. Do it yourself: with a Stored-Token (with an expiration date-time)
  2. Do it yourself: with a Signed-GlobalID from Rails (self-times out & no stored tokens)
  3. Other Options: other Gems for Devise, Sorcery, or independent gems


  1. User enters their email-address in a simple form
  2. If account is found - a link with a token is generated and email is sent
  3. User is notified that the link is on its way (even if the account is not found and no email is sent)
  4. When the user follows the link in the email, a session is generated
  5. Session valid until the session expires or the user logs out (deleting the session).

NOTE: User accounts are assumed to be previously created, and verified. If you need a full set of features - then your best option is probably to use devise, sorcery or authenticate and use an extension or build your own extension to one of these libraries. Either way, this article will clarify the basics of passwordless authentication.

Getting Started

Code Repo is posted at: https://github.com/btihen/magic_sgid

Create a Rails Project

bin/rails new magic_id
cd magic_id
git add .
git commit -m "initial commit on creation"

User-Controller to manage users:

bin/rails db:create
bin/rails g scaffold User name:string email:string
bin/rails db:migrate

Lets start Rails

bin/rails s

Go to: http://localhost:3000/users and create a few users - feel free to make the GUI nicer!

Assuming all is good:

git add .
git commit "user management scaffold"

Create a Landing Page

we need a landing / root page to send users when they are not logged in:

bin/rails g controller landing index

now lets point the root page to that too - make the routes page look like:

# config/routes.rb
Rails.application.routes.draw do
  get '/landing', to: 'landing#index', as: :landing
  root to: "landing#index"

I will also remove: app/helpers/landing_helper.rb with:

rm app/helpers/landing_helper.rb

Now lets check all is well with the routes:

bin/rails routes | grep landing
# should show
  landing GET /landing(:format) landing#index
     root GET /                 landing#index

(quite likely it will be all spread out)

Now the following pages should be available:

  • http://localhost:3000/
  • http://localhost:3000/landing

again feel free to make them look nice.

assuming all works well:

git add .
git commit -m "create landing page and landing & root route"

Create a User Application Controller (restrict access)

This will allow us to control access to all urls in the /users paths within our app

mkdir app/controllers/users
touch app/controllers/users/application_controller.rb

The application controller ensures only authenticated users (with a session) can access pages in the users area:

# app/controllers/users/application_controller.rb
class Users::ApplicationController < ApplicationController
  before_action :users_only

  def current_user(user_id = session[:user_id])
    # `try` and `find_by` avoid raising an exception w/o a session
    @current_user ||= User.find_by(id: user_id)


  # code to ensure only logged in users have access to users pages
  def users_only
    # send person to a safe page if not logged in
    if current_user.blank?
      # send to login page to get an access link
      redirect_back(fallback_location: landing_path,
                    :alert => "Login Required")
      # once the below page is created we can redirect to here instead
      # redirect_back(fallback_location: new_users_login_path,
      #               :alert => "Login Required")

NOTE: if you want all pages protected then put this code in: app/controllers/application_controller.rb and adjust the routes (remove the namespace)!

Restricted User Home Page

we need a landing / root page to send users when they are not logged in:

bin/rails g controller users/landing index

now lets point the root page to that too - make the routes page look like:

# config/routes.rb
Rails.application.routes.draw do
  namespace :users do
    get '/',                as: 'root',         to: 'home#index'
    get '/home',            as: 'home',         to: 'home#index'
  get '/landing', to: 'landing#index', as: :landing
  root to: "landing#index"

Update the controller to use the Users::ApplicationController:

# app/controllers/users/home_controller.rb
class Users::HomeController < Users::ApplicationController
  def index

I will also remove: app/helpers/users/home_helper.rb with:

rm app/helpers/users/home_helper.rb

Now lets check all is well with the routes:

bin/rails routes | grep user
# should show
  users_home GET /users/home(:format) home#index

(quite likely it will be all spread out)

Now the following pages should NOT be available:

  • http://localhost:3000/users
  • http://localhost:3000/users/home

and we should be redirected to the landing page. If you access the home page - then probably the first line is wrong it should be:

Users::HomeController < Users::ApplicationController

assuming all works well:

git add .
git commit -m "create restricted user home page"

Create an Session Authorization Controller

touch app/controllers/users/sessions_controller.rb
class Users::SessionsController < Users::ApplicationController
  # before_action :users_only, only: :destroy
  skip_before_action :users_only, only: :create

  def create
    sgid_token = params[:token].to_s
    user = GlobalID::Locator.locate_signed(sgid_token, for: 'user_access')
    if user
      # create the session id for current_user to access
      session[:user_id] = user.id
      redirect_to(users_home_path, notice: "Welcome back #{user.name}")
      flash[:alert] = 'Oops - you need a new login link'
      # later when created we will redirect to login access link page
      # redirect_to(new_users_login)

  # allow a user to logout / destroy session if desired
  def destroy
    user = current_user
    if user
      session[:user_id] = nil
      flash[:notice] = "logout successful"
      falsh[:alert] = "Oops, there was a problem"

Add to routes:

# config/routes.rb
Rails.application.routes.draw do
  namespace :users do
    get '/',                as: 'root',         to: 'home#index'
    get '/home',            as: 'home',         to: 'home#index'
    # use get to create since I don't think a text url can create a post
    get '/sessions/:token', as: 'session_create', to: 'sessions#create'
    # allow logout / destroy the session
    resources :sessions,    only: [:destroy]
  get '/landing', to: 'landing#index', as: :landing
  root to: "landing#index"

To test this go to rails console:

bin/rails c
# create our own token
user = User.first
global_id = User.find(user.id).to_sgid(expires_in: 1.hour, for: 'user_access')
access_token = global_id.to_s

# check that this global_id works (we should get the same user)
GlobalID::Locator.locate_signed(access_token, for: 'user_access')

# add url helpers to console
include ActionView::Helpers
include ActionView::Helpers::UrlHelper
# generate the URL for the session
Rails.application.routes.url_helpers.users_session_create_url(token: global_id.to_s, host: 'locahost:3000')
# should get something like:
# "http://locahost:3000/users/sessions/BAh7CEkiCGdpZAY6BkVUSSItZ2lkOi8vbWFnaWMtbGlua3MvVXNlci8xP2V4cGlyZXNfaW49MzYwMAY7AFRJIgxwdXJwb3NlBjsAVEkiEHVzZXJfYWNjZXNzBjsAVEkiD2V4cGlyZXNfYXQGOwBUSSIdMjAyMS0wOS0xOVQxNTozNzo0MS4wNjdaBjsAVA==--c948a0a5ccbae391c7ab9c808677fe41da4cbc28"

# copy this url into the browser
# now we be on: `http://localhost:3000/user/` & `http://localhost:3000/user/home`

# if you try again in an hour it should not work!

Note: by default rails sessions have no expiration, thus are deleted when the browser closes. To change this default behavior, you can set the session length with the setting:

# config/initializers/session_store.rb
Rails.application.config.session_store :cookie_store, expire_after: 14.days

Assuming all works:

git add .
git commit -m "session controller gives access to users_home"

We will need to allow the user to request an access-link. We will do this with (we won’t be generating any models just a controller and a submission form - scaffold_controller does this for us):

We need a way to send the login link - so we will create a login mailer with:

bin/rails generate mailer Login send_link

Configure our emailer for our needs with:

class LoginMailer < ApplicationMailer
  def send_link(user, login_url)
    @user = user
    @login_url  = login_url
    host = Rails.application.config.hosts.first

    mail(to: @user.email, subject: "Access-Link for #{host}")

And of course set up the views that contain the contents of the email: The HTML Version

# app/views/login_mailer/send_link.html.erb
<h1>Hi <%= @user.name %>,</h1>

<p><a href="<%= @login_url %>">Access-Link for <%= @host %></a></p>

<p> <%= @login_url %> </p>

<p>Link is valid for about an hour from <%= DateTime.now %></p>

The text version:

# app/views/login_mailer/send_link.text.erb
Hi <%= @user.name %>,

Access-Link for <%= @host %> is:

<%= @login_url %>

Link is valid for about an hour from <%= DateTime.now %>.

Setup Mailhog (OPTIONAL)

This is optional - technical testing can be done from the log file - but to see what the email formatting looks like this is VERY HELPFUL.

brew install mailhog

Configure Rails to send emails to port 1025 in development (where mailhog listens)

# config/environments/development.rb
Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.
  # ...
  # mailhog config
  config.action_mailer.perform_deliveries = true
  config.action_mailer.smtp_settings = { address: 'localhost', port: 1025 }
  # ...

now open - to view:

open localhost:8025


Now lets create a user login controller:

touch app/controllers/users/logins_controller.rb

Add the contents of the controller:

# app/controllers/users/logins_controller.rb
class Users::LoginsController < Users::ApplicationController
skip_before_action :users_only

  def new
    user = User.new
    render :new, locals: {user: user}

  def create
    email = user_params[:email]
    ip_address = request.remote_ip
    # the participant might already exist in our db or possimagic_link_url = participants_session_auth_url(token: participant.login_token)bly a new participant
    user = User.find_by(email: email)

    if user
      # create a signed expiring Rails Global ID - this makes LONG tokens, but browswers can handle it
      # all browsers should handle up to 2000 characters.
      # https://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url-in-different-browsers
      # https://www.geeksforgeeks.org/maximum-length-of-a-url-in-different-browsers/
      global_id = user.to_sgid(expires_in: 1.hour, for: 'user_access')
      access_url = users_session_create_url(token: global_id.to_s)
      LoginMailer.send_link(user, access_url).deliver_later
      # if user isn't found then grab a user and compute the global_id and url (but don't send an email)
      # in order to make the time of both paths similar - so people can't find user emails checking the response times
      # see: https://abevoelker.com/skipping-the-database-with-stateless-tokens-a-hidden-rails-gem-and-a-useful-web-technique/

      global_id = User.first.to_sgid(expires_in: 1.hour, for: 'user_access')
      access_url = user_auth_url(token: global_id.to_s)

    # uncomment to add noise to further make email fishing difficult to time
    # mini_wait = Random.new.rand(10..20) / 1000
    # wait(mini_wait)

    # true or not we state we have sent an access link and redirect to the landing page
    # also prevent email fishing by always returning the same answer
    redirect_to(landing_path, notice: "Access-Link has been sent")


    # Only allow a list of trusted parameters through.
    def user_params

NOTE: You can let the GlobalID be valid for however long you want (in hours), but since email isn’t very secure, it seems wise to keep this short lived. The default time is 30.days

We need to add the route to the users login_controller with:

# config/routes.rb
Rails.application.routes.draw do
  # restricted area (protected by user login - Users::ApplicationController)
  namespace :users do
    get '/',                as: 'root',         to: 'home#index'
    get '/home',            as: 'home',         to: 'home#index'
    # use get to create since I don't think a text url can create a post
    get '/sessions/:token', as: 'session_create', to: 'sessions#create'
    # allow logout / destroy the session
    resources :sessions,    only: [:destroy]
    # login (generates link and emails to the user)
    resources :logins,      only: [:new, :create]
  get '/landing', to: 'landing#index', as: :landing
  root to: "landing#index"

now check the routes:

bin/rails routes | grep users
# should return
     users_logins POST  /users/logins(.:format)     users/logins#create
  new_users_login GET   /users/logins/new(.:format) users/logins#new

Login email form:

mkdir app/views/users/logins
touch app/views/users/logins/new.html.erb

Note I often use Bulma - so here is how I like to format my forms (without Bulma installed the form will be ugly). Also note, I dislike using instance variables in my form - so this is why the form looks a little extra complicated.

# app/views/users/logins/new.html.erb
<%= form_for(user, local: true,
             url: users_logins_path,   # NEW MUST BE PLURAL for POST
             id: "user-login-form", class: "user" ) do |form|  %>

  <div class="field">
    <label class="label">Email for Access-Link</label>
    <div class="control">
      <%= form.email_field :email,
                            placeholder: "Email",
                            class: 'input' %>
    <p class="help"></p>

  <div class="control">
    <%= form.submit("Get Access-Link", class: "button is-success") %>

<% end  %>

Test the full flow

using the command line create some users:

bin/rails c
User.create(email: "tester@test.ch", name: "Tester")

start rails with: bin/rails s start mailhog with: mailhog go to: http://localhost:3000/user/home (should get redirected to the below URL) go to: http://localhost:3000/user/logins enter the “tester@test.ch” email Check mailhog for the link http://localhost:8025/ Click the link you should now be on http://localhost:3000/user/home

Assuming everything works:

git add .
git commit -m "working magic links using Rails Global ID"

NOTE: obviously automated tests are important (both spec and feature tests).


Rails GlobalID

The nice thing about these is that the auto expire - simplifying the code a lot.

Token using SecureRandom

With these you need to create your own expiration and lookup system (more code add a migration), but will work with any framework.

Devise Options

Other Options


Bill Tihen
Bill Tihen
Developer, Data Enthusiast, Educator and Nature’s Friend

very curious – known to explore knownledge and nature