Add new fields to Devise model. Rails 5

Customizing the RegistrationsController

class RegistrationsController < Devise::RegistrationsController

  private

  def sign_up_params
    params.require(:user).permit(:first_name, :last_name, :email, :password, :password_confirmation)
  end

  def account_update_params
    params.require(:user).permit(:first_name, :last_name, :email, :password, :password_confirmation, :current_password)
  end
end

Now we need to tell Devise to use our registrations controller - we can do this in our config/routes.rb file.

devise_for :users, :controllers => { registrations: 'registrations' }