heartcombo--devise/lib/devise/hooks/timeoutable.rb

# Each time a record is set we check whether its session has already timed out
# or not, based on last request time. If so, the record is logged out and
# redirected to the sign in page. Also, each time the request comes and the
# record is set, we set the last request time inside it's scoped session to
# verify timeout in the following request.
Warden::Manager.after_set_user do |record, warden, options|
  scope = options[:scope]
  if record && record.respond_to?(:timedout?) && warden.authenticated?(scope)
    last_request_at = warden.session(scope)['last_request_at']

    if record.timedout?(last_request_at)
      warden.logout(scope)
      throw :warden, :scope => scope, :message => :timeout
    end

    warden.session(scope)['last_request_at'] = Time.now.utc
  end
end