Try signing in the user after user confirmation is correct and redirect to…

app/controllers/confirmations_controller.rb

+class ConfirmationsController < Devise::ConfirmationsController
+
+  protected
+
+  def after_confirmation_path_for(resource_name, resource)
+    if signed_in?(resource_name)
+      signed_in_root_path(resource)
+    else
+      sign_in(resource)
+      if signed_in?(resource_name)
+        signed_in_root_path(resource)
+      else
+        new_session_path(resource_name)
+      end
+    end
+  end
+end

config/routes.rb

@@ -170,7 +170,7 @@ Gitlab::Application.routes.draw do
 
   resources :projects, constraints: { id: /[^\/]+/ }, only: [:new, :create]
 
-  devise_for :users, controllers: { omniauth_callbacks: :omniauth_callbacks, registrations: :registrations , passwords: :passwords, sessions: :sessions }
+  devise_for :users, controllers: { omniauth_callbacks: :omniauth_callbacks, registrations: :registrations , passwords: :passwords, sessions: :sessions, confirmations: :confirmations }
 
   devise_scope :user do
     get "/users/auth/:provider/omniauth_error" => "omniauth_callbacks#omniauth_error", as: :omniauth_error