Can't permit parameters in rails engine

[steffenschmidt]

I have a rails 5 api only app where I use devise_token_auth in my core engine. Unfortunately I cannot set parameters which I would allow to set in registration process

rails (5.0.0.1)
devise (4.2.0)
devise_token_auth (0.1.39)

That is my engine application controller (RAILS_ROOT/engines/core/app/controllers/project_name/application_controller.rb):

module ProjectName
  class ApplicationController < ActionController::Base
    protect_from_forgery with: :null_session

    include DeviseTokenAuth::Concerns::SetUserByToken

    before_action :configure_permitted_parameters, if: :devise_controller?

  protected

    def configure_permitted_parameters
      devise_parameter_sanitizer.permit(:sign_up, keys: [:name])
    end

  end
end

That is my user model inside my engine (RAILS_ROOT/engines/core/app/models/project_name/user.rb):

module ProjectName
  class User < ApplicationRecord
    devise :database_authenticatable, :registerable,
           :recoverable, :rememberable, :trackable, :validatable

    include DeviseTokenAuth::Concerns::User

    validates :name, presence: true
  end
end

My routes are set to the following:

ProjectName::Core::Engine.routes.draw do
  mount_devise_token_auth_for "ProjectName::User", at: "auth"
end

When requesting the route to create an user I get the following info in the log file:

Started POST "/auth" for ::1 at 2016-09-11 16:36:52 +0200
Processing by DeviseTokenAuth::RegistrationsController#create as JSON
  Parameters: {"email"=>"[email protected]", "password"=>"[FILTERED]", "name"=>"Test User", "registration"=>{"email"=>"[email protected]", "password"=>"[FILTERED]", "name"=>"Test User"}}
Unpermitted parameters: name, registration

I realized that the before_action configure_permitted_parameters will not be called. But why? Even if I remove the if-condition the engine controller ignores the method.

How can I allow a users name in the registration process? Can anyone help me? Thanks in advance?

[steffenschmidt]

I solved this by setting config.parent_controller = "ProjectName::ApplicationController" to my devise.rb initializer.