strong_params.rb

class PeopleController < ActionController::Base
  # This will raise an ActiveModel::ForbiddenAttributes exception because it's using mass assignment
  # without an explicit permit step.
  def create
    Person.create(params[:person])
  end

  # This will pass with flying colors as long as there's a person key in the parameters, otherwise
  # it'll raise a ActionController::MissingParameter exception, which will get caught by 
  # ActionController::Base and turned into that 400 Bad Request reply.
  def update
    redirect_to current_account.people.find(params[:id]).tap do |person|
      person.update_attributes!(person_params)
    end
  end

  private
    # Using a private method to encapsulate the permissible parameters is just a good pattern
    # since you'll be able to reuse the same permit list between create and update. Also, you
    # can specialize this method with per-user checking of permissible attributes.
    def person_params
      params.required(:person).permit(:name, :age)
    end
end