class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception
  helper_method :resource_name, :resource, :devise_mapping
  def resource_name
      :user
    end

    def resource
      @resource ||= User.new
    end

    def devise_mapping
      @devise_mapping ||= Devise.mappings[:user]
    end
end

class ApplicationController < ActionController::Base
  # Prevent CSRF attacks by raising an exception.
  # For APIs, you may want to use :null_session instead.
  protect_from_forgery with: :exception
  helper_method :resource_name, :resource, :devise_mapping
  skip_before_action :verify_authenticity_token, if: :json_request?
  def resource_name
    :user
  end

  def resource
    @resource ||= User.new
  end

  def devise_mapping
    @devise_mapping ||= Devise.mappings[:user]
  end

  protected
  def json_request?
    request.format.json?
  end

end

Disable CSRF for JSON API
Disable CSRF for JSON API
