def make_expires(sec=nil)
      case sec
      when Numeric
        Time.now + sec
      when true
        Time.at(1)
      when nil
        Time.at(2**31-1)
      end
    end
def make_expires(sec=nil)
      case sec
      when Numeric
        Time.now + sec
      when true
        Time.at(1)
      when nil
        Time.at(2**31-1)
      end
    end
Returns an expiry Time based on +sec+ which can be one of:
 Numeric:: +sec+ seconds into the future
 +true+::  the expiry time is the start of 1970 (i.e. expired)
 +nil+::   it is  Tue Jan 19 03:14:07 GMT Standard Time 2038 (i.e. when
           UNIX clocks will die)