def cram_md5_response(secret, challenge)
      tmp = Digest::MD5.digest(cram_secret(secret, IMASK) + challenge)
      Digest::MD5.hexdigest(cram_secret(secret, OMASK) + tmp)
    end
def cram_md5_response(secret, challenge)
      tmp = Digest::MD5.digest(cram_secret(secret, IMASK) + challenge)
      Digest::MD5.hexdigest(cram_secret(secret, OMASK) + tmp)
    end
CRAM-MD5: [RFC2195]