class Net::IMAP::SASL::DigestMD5Authenticator

def compute_a2(response)
  a2 = "AUTHENTICATE:#{response[:"digest-uri"]}"
  if response[:qop] and response[:qop] =~ /^auth-(?:conf|int)$/
    a2 << ":00000000000000000000000000000000"
  end
  a2
end