```ruby
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController

  def google_oauth2
    # You need to implement the method below in your model (e.g. app/models/user.rb)
    @user = User.from_omniauth(request.env["omniauth.auth"])

    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.google_data"] = request.env["omniauth.auth"].except(:extra) #Removing extra as it can overflow some session stores
      redirect_to new_user_registration_url, alert: @user.errors.full_messages.join("\n")
    end
  end

  def failure
    sign_out current_user unless current_user.nil?
    redirect_to root_path, notice: t(:login_error)
  end

end
```

Update login process to avoid it for logged users
user
```ruby
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController

  def google_oauth2
    redirect_to services_path unless current_user.nil?
    # You need to implement the method below in your model (e.g. app/models/user.rb)
    @user = User.from_omniauth(request.env["omniauth.auth"])
    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication
    else
      session["devise.google_data"] = request.env["omniauth.auth"].except(:extra) #Removing extra as it can overflow some session stores
      redirect_to new_user_registration_url, alert: @user.errors.full_messages.join("\n")
    end
  end

  def failure
    sign_out current_user unless current_user.nil?
    redirect_to root_path, notice: t(:login_error)
  end

end
```
assistant