class AWS::S3::PresignedPost

def format_expiration
  time = expires || Time.now.utc + 60*60
  time =
    case time
    when Time
      time
    when DateTime
      Time.parse(time.to_s)
    when Integer
      (Time.now + time)
    when String
      Time.parse(time)
    end
  time.utc.iso8601
end