class Net::IMAP::SASL::DigestMD5Authenticator

def compute_a1(response)
  a0 = compute_a0(response)
  a1 = [ a0, response.values_at(:nonce, :cnonce) ].join(":")
  a1 << ":#{response[:authzid]}" unless response[:authzid].nil?
  a1
end