france_connect: make existing user lookup case-insensitive

Fix #4053

app/controllers/france_connect/particulier_controller.rb

@@ -13,7 +13,7 @@ class FranceConnect::ParticulierController < ApplicationController
         fetched_fci.tap(&:save)
 
     if fci.user.nil?
-      user = User.find_or_create_by(email: fci.email_france_connect) do |new_user|
+      user = User.find_or_create_by(email: fci.email_france_connect.downcase) do |new_user|
         new_user.password = Devise.friendly_token[0, 20]
         new_user.confirmed_at = Time.zone.now
       end

spec/controllers/france_connect/particulier_controller_spec.rb

@@ -85,6 +85,17 @@ describe FranceConnect::ParticulierController, type: :controller do
               expect(subject).to redirect_to(root_path)
             end
           end
+
+          context 'when a differently cased email address is already used' do
+            let(:email) { 'TEST@test.com' }
+            let!(:user) { create(:user, email: email.downcase, france_connect_information: nil) }
+
+            it 'associates the france_connect infos with the existing user' do
+              expect { subject }.not_to change(User, :count)
+              expect(user.reload.loged_in_with_france_connect).to eq(User.loged_in_with_france_connects.fetch(:particulier))
+              expect(subject).to redirect_to(root_path)
+            end
+          end
         end
       end