overriding the registrations controller

en.yml

# Sample localization file for English. Add more files in this directory for other locales.
# See https://github.com/svenfuchs/rails-i18n/tree/master/rails%2Flocale for starting points.

en:
  hello: "Hello world"
  mailboxer:
    message_mailer:
      subject_new: "new %{type} from %{sender}"
      subject_reply: "new %{type} from %{sender}"
en:
  devise:
    registrations:
      destroyed: "Bye! Your account was successfully cancelled. We hope to see you again soon."
      signed_up: ""
      signed_in: ""
      signed_out: ""
      signed_up_but_inactive: "You have signed up successfully. However, we could not sign you in because your account is not yet activated."
      signed_up_but_locked: "You have signed up successfully. However, we could not sign you in because your account is locked."
      signed_up_but_unconfirmed: "A message with a confirmation link has been sent to your email address. Please open the link to activate your account."
      update_needs_confirmation: "You updated your account successfully, but we need to verify your new email address. Please check your email and click on the confirm link to finalize confirming your new email address."
      updated: "You updated your account successfully."
    sessions:
      signed_in: ""
      signed_out: ""

registrations_controller.rb

class RegistrationsController < Devise::RegistrationsController
  prepend_before_filter :allow_params_authentication!, :only => :create
  
  def create
    user_exists = User.exists?(email: params[:user][:email])

    if user_exists
      build_resource(sign_up_params)

      self.resource = warden.authenticate!(auth_options)
      set_flash_message(:notice, :signed_in) if is_flashing_format?
      sign_in(resource_name, resource)
      yield resource if block_given?
      respond_with resource, :location => after_sign_in_path_for(resource)
    else
      build_resource(sign_up_params)

      if resource.save
        yield resource if block_given?
        if resource.active_for_authentication?
          set_flash_message :notice, :signed_up if is_flashing_format?
          sign_up(resource_name, resource)
          respond_with resource, :location => after_sign_up_path_for(resource)
        else
          set_flash_message :notice, :"signed_up_but_#{resource.inactive_message}" if is_flashing_format?
          expire_data_after_sign_in!
          respond_with resource, :location => after_inactive_sign_up_path_for(resource)
        end
      else
        clean_up_passwords resource
        respond_with resource
      end
    end
  end

  protected

  def sign_in_params
    devise_parameter_sanitizer.sanitize(:sign_in)
  end

  def serialize_options(resource)
    methods = resource_class.authentication_keys.dup
    methods = methods.keys if methods.is_a?(Hash)
    methods << :password if resource.respond_to?(:password)
    { :methods => methods, :only => [:password] }
  end

  def auth_options
    { :scope => resource_name, :recall => "#{controller_path}#new" }
  end

end

routes.rb

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

helpful discussion found here: heartcombo/devise#1230