some_class.rb

class SomeClass
  def initialize(current_account, form, request)
    @form = form
    @request = request
  end

  def call
    return broadcast(:invalid, form) if invalid?

    auth_header ||= user.create_new_auth_token
    user.update_tracked_fields!(request)

    broadcast(:ok, auth_header, user)
  end

  private

  attr_reader :form, :request

  def invalid?
    form.invalid? || invalid_credentials?
  end

  def invalid_credentials?
    return false if user.present?

    form.errors.add(:credentials, :invalid)
  end

  def user
    @user ||= ::User.authenticate(:email => form.email, :password => form.password)
  end
end