Ruby On Rails: Login
By Josh Cunningham 
This tutorial demonstrates how to add user login to a Ruby on Rails application. We recommend you to Log in to follow this quickstart with examples configured for your account.
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How it works
Configure Auth0
How to implement it
Get Your Application Keys
When you signed up for Auth0, a new application was created for you, or you could have created a new one.
You will need some details about that application to communicate with Auth0. You can get these details from the Application Settings section in the Auth0 dashboard.
You need the following information:
- Domain
- Client ID
- Client Secret
Keep reading
Configure Callback URLs
A callback URL is a URL in your application where Auth0 redirects the user after they have authenticated.
The callback URL for your app must be whitelisted in the Allowed Callback URLs field in your Application Settings. If this field is not set, users will be unable to log in to the application and will get an error.
Configure Logout URLs
A logout URL is a URL in your application that Auth0 can return to after the user has been logged out of the authorization server. This is specified in the returnTo query parameter.
The logout URL for your app must be whitelisted in the Allowed Logout URLs field in your Application Settings. If this field is not set, users will be unable to log out from the application and will get an error.
Configure Rails to Use Auth0
Install the Dependencies
To follow along with this guide, add the following dependencies to your Gemfile:
To prevent forged authentication requests, we need to also include CSRF protection. If you're using OmniAuth with Rails, include:
Once your gems are added, install with the following command:
Initialize OmniAuth Auth0
Create a file named auth0.rb under config/initializers and configure the OmniAuth middleware in it.
Add the Auth0 Callback Handler
Use the following command to create the controller that will handle the Auth0 callback:
In the newly created controller, add success and failure callback handlers.
Replace the generated routes with the following:
Trigger Authentication
We need a way for users to trigger authentication. Add a link to /auth/auth0 anywhere in an existing template or use the steps below to generate a homepage in a new app.
Run the following command to generate the homepage controller and views:
Add the following to the generated show.html.erb file:
Finally, point the root path to generated controller:
Run bin/rails server and go to localhost:3000 in your browser. You should see the Auth0 logo and a link to log in.
Check the User's Authentication Status
You can use a controller concern to control access to routes that require the user to be authenticated:
Now generate a controller for the dashboard view that users will see once they are authenticated:
Include the concern in the this new controller to prevent unauthenticated users from accessing its routes:
Add the session data for userinfo to the dashboard view to see what is returned:
Finally, adjust your routes to point /dashboard to this new, secured controller:
With the Rails server still running, go to localhost:3000/dashboard in your browser and you should be redirected to the homepage.
Click the Login link and log in or sign up. Accept the consent modal that appears (for localhost only) and you should end up on at /dashboard with your user info showing.
Display Error Descriptions
Configure the application to display errors by adding the following to the production environment config:
Troubleshooting
Using a reverse proxy
The redirect_uri parameter that OmniAuth generates when redirecting to login is based on the Host header that is passed to Rails. This can cause incorrect callback URLs to be passed when using this strategy (and OmniAuth in general) with a reverse proxy. You can adjust the host used by OmniAuth with the following snippet:
See this StackOverflow thread for more information.
ActionController::InvalidAuthenticityToken
This is likely caused by a missing CSRF token needed to POST the login request. If you inspect the login button in your browser, you should see something like this:
... and in the <head> element for the page, you should have CSRF meta tags like these:
With those elements in place, Rails will convert the login link to POST the CSRF token to the backend to verify it before redirecting to login.
This error means that a cookie session is being used and because the whole profile is being stored, it overflows the max-size of 4 kb. If you are unable to access the user profile and you get an error similar to NoMethodError, undefined method '[]' for nil:NilClass, try using In-Memory store for development.
Go to /config/initializers/session_store.rb and add the following:
Go to /config/environments/development.rb and add the following:
It is recommended that a memory store such as MemCached being used for production applications.
SSL Issues
Under some configurations, Ruby may not be able to find certification authority certificates (CA certs).
Download the CA certs bundle to the project directory:
Add this initializer to config/initializers/fix_ssl.rb:
"failure message=invalid_credentials"
This issue doesn't occur when working locally but may happen in a staging or production environment. The error message may be displayed as:
To solve this, add the following to config/environments/staging.rb or production.rb:
Substitute http://www.example.com with the actual URL you'll be using in your application.