// be stored in the critical options.
		if len(attribValue) != 1 {
			continue
		}

		if attribKey == "sshPublicKey" && key != nil {
			key2, _, _, _, err := ssh.ParseAuthorizedKey([]byte(attribValue[0]))
			if err != nil {
				return nil, errSFTPPublicKeyBadFormat
			}

			if subtle.ConstantTimeCompare(key2.Marshal(), key.Marshal()) != 1 {
				return nil, errAuthentication
			}