OmniAuth

The rodauth-omniauth gem provides login and registration functionality with multiple providers using OmniAuth, together with persistence of external identities.

Let's assume we're building Facebook login, and we've already set up a Facebook OAuth 2.0 application for our project. We'll start by installing the necessary gems:

$ bundle add rodauth-omniauth omniauth-facebook

Let's save Facebook app key and secret in our project credentials:

$ rails credentials:edit

# ...
facebook:
  app_id: "<YOUR_APP_ID>"
  app_secret: "<YOUR_APP_SECRET>"

We'll also create the identities table required by rodauth-omniauth:

$ rails generate migration create_account_identities
$ rails db:migrate

# db/migrate/*_create_account_identities.rb
class CreateAccountIdentities < ActiveRecord::Migration
  def change
    create_table :account_identities do |t|
      t.references :account, foreign_key: { on_delete: :cascade }
      t.string :provider, null: false
      t.string :uid, null: false
      t.index [:provider, :uid], unique: true
    end
  end
end

Now we can register the facebook strategy in our Rodauth configuration:

# app/misc/rodauth_main.rb
class RodauthMain < Rodauth::Rails::Auth
  configure do
    enable :omniauth

    omniauth_provider :facebook,
      Rails.application.credentials.facebook[:app_id],
      Rails.application.credentials.facebook[:app_secret],
      scope: "email"
  end
end

Finally, we can add the Facebook login button to our login form:

$ rails generate rodauth:views login

<!-- app/views/rodauth/_login_form_footer.html.erb -->
<!-- ... -->
  <li>
    <%= button_to "Login via Facebook", rodauth.omniauth_request_path(:facebook),
      method: :post, data: { turbo: false }, class: "btn btn-link p-0" %>
  </li>
<!-- ... -->