// Package rfc2136 implements a DNS provider for solving the DNS-01 challenge using the rfc2136 dynamic update. package rfc2136 import ( "errors" "fmt" "net" "strings" "time" "github.com/go-acme/lego/v4/challenge/dns01" "github.com/go-acme/lego/v4/platform/config/env" "github.com/miekg/dns" ) // Environment variables names. const ( envNamespace = "RFC2136_" EnvTSIGKey = envNamespace + "TSIG_KEY" EnvTSIGSecret = envNamespace + "TSIG_SECRET" EnvTSIGAlgorithm = envNamespace + "TSIG_ALGORITHM" EnvNameserver = envNamespace + "NAMESERVER" EnvDNSTimeout = envNamespace + "DNS_TIMEOUT" EnvTTL = envNamespace + "TTL" EnvPropagationTimeout = envNamespace + "PROPAGATION_TIMEOUT" EnvPollingInterval = envNamespace + "POLLING_INTERVAL" EnvSequenceInterval = envNamespace + "SEQUENCE_INTERVAL" ) // Config is used to configure the creation of the DNSProvider. type Config struct { Nameserver string TSIGAlgorithm string TSIGKey string TSIGSecret string PropagationTimeout time.Duration PollingInterval time.Duration TTL int SequenceInterval time.Duration DNSTimeout time.Duration } // NewDefaultConfig returns a default configuration for the DNSProvider. func NewDefaultConfig() *Config { return &Config{ TSIGAlgorithm: env.GetOrDefaultString(EnvTSIGAlgorithm, dns.HmacSHA1), TTL: env.GetOrDefaultInt(EnvTTL, dns01.DefaultTTL), PropagationTimeout: env.GetOrDefaultSecond(EnvPropagationTimeout, env.GetOrDefaultSecond("RFC2136_TIMEOUT", 60*time.Second)), PollingInterval: env.GetOrDefaultSecond(EnvPollingInterval, 2*time.Second), SequenceInterval: env.GetOrDefaultSecond(EnvSequenceInterval, dns01.DefaultPropagationTimeout), DNSTimeout: env.GetOrDefaultSecond(EnvDNSTimeout, 10*time.Second), } } // DNSProvider implements the challenge.Provider interface. type DNSProvider struct { config *Config } // NewDNSProvider returns a DNSProvider instance configured for rfc2136 // dynamic update. Configured with environment variables: // RFC2136_NAMESERVER: Network address in the form "host" or "host:port". // RFC2136_TSIG_ALGORITHM: Defaults to hmac-md5.sig-alg.reg.int. (HMAC-MD5). // See https://github.com/miekg/dns/blob/master/tsig.go for supported values. // RFC2136_TSIG_KEY: Name of the secret key as defined in DNS server configuration. // RFC2136_TSIG_SECRET: Secret key payload. // RFC2136_PROPAGATION_TIMEOUT: DNS propagation timeout in time.ParseDuration format. (60s) // To disable TSIG authentication, leave the RFC2136_TSIG* variables unset. func NewDNSProvider() (*DNSProvider, error) { values, err := env.Get(EnvNameserver) if err != nil { return nil, fmt.Errorf("rfc2136: %w", err) } config := NewDefaultConfig() config.Nameserver = values[EnvNameserver] config.TSIGKey = env.GetOrFile(EnvTSIGKey) config.TSIGSecret = env.GetOrFile(EnvTSIGSecret) return NewDNSProviderConfig(config) } // NewDNSProviderConfig return a DNSProvider instance configured for rfc2136. func NewDNSProviderConfig(config *Config) (*DNSProvider, error) { if config == nil { return nil, errors.New("rfc2136: the configuration of the DNS provider is nil") } if config.Nameserver == "" { return nil, errors.New("rfc2136: nameserver missing") } if config.TSIGAlgorithm == "" { config.TSIGAlgorithm = dns.HmacSHA1 } // Append the default DNS port if none is specified. if _, _, err := net.SplitHostPort(config.Nameserver); err != nil { if strings.Contains(err.Error(), "missing port") { config.Nameserver = net.JoinHostPort(config.Nameserver, "53") } else { return nil, fmt.Errorf("rfc2136: %w", err) } } if config.TSIGKey == "" || config.TSIGSecret == "" { config.TSIGKey = "" config.TSIGSecret = "" } return &DNSProvider{config: config}, nil } // Timeout returns the timeout and interval to use when checking for DNS propagation. // Adjusting here to cope with spikes in propagation times. func (d *DNSProvider) Timeout() (timeout, interval time.Duration) { return d.config.PropagationTimeout, d.config.PollingInterval } // Sequential All DNS challenges for this provider will be resolved sequentially. // Returns the interval between each iteration. func (d *DNSProvider) Sequential() time.Duration { return d.config.SequenceInterval } // Present creates a TXT record using the specified parameters. func (d *DNSProvider) Present(domain, token, keyAuth string) error { info := dns01.GetChallengeInfo(domain, keyAuth) err := d.changeRecord("INSERT", info.EffectiveFQDN, info.Value, d.config.TTL) if err != nil { return fmt.Errorf("rfc2136: failed to insert: %w", err) } return nil } // CleanUp removes the TXT record matching the specified parameters. func (d *DNSProvider) CleanUp(domain, token, keyAuth string) error { info := dns01.GetChallengeInfo(domain, keyAuth) err := d.changeRecord("REMOVE", info.EffectiveFQDN, info.Value, d.config.TTL) if err != nil { return fmt.Errorf("rfc2136: failed to remove: %w", err) } return nil } func (d *DNSProvider) changeRecord(action, fqdn, value string, ttl int) error { // Find the zone for the given fqdn zone, err := dns01.FindZoneByFqdnCustom(fqdn, []string{d.config.Nameserver}) if err != nil { return err } // Create RR rr := new(dns.TXT) rr.Hdr = dns.RR_Header{Name: fqdn, Rrtype: dns.TypeTXT, Class: dns.ClassINET, Ttl: uint32(ttl)} rr.Txt = []string{value} rrs := []dns.RR{rr} // Create dynamic update packet m := new(dns.Msg) m.SetUpdate(zone) switch action { case "INSERT": // Always remove old challenge left over from who knows what. m.RemoveRRset(rrs) m.Insert(rrs) case "REMOVE": m.Remove(rrs) default: return fmt.Errorf("unexpected action: %s", action) } // Setup client c := &dns.Client{Timeout: d.config.DNSTimeout} // TSIG authentication / msg signing if d.config.TSIGKey != "" && d.config.TSIGSecret != "" { key := strings.ToLower(dns.Fqdn(d.config.TSIGKey)) alg := dns.Fqdn(d.config.TSIGAlgorithm) m.SetTsig(key, alg, 300, time.Now().Unix()) // secret(s) for Tsig map[<zonename>]<base64 secret>, // zonename must be in canonical form (lowercase, fqdn, see RFC 4034 Section 6.2) c.TsigSecret = map[string]string{key: d.config.TSIGSecret} } // Send the query reply, _, err := c.Exchange(m, d.config.Nameserver) if err != nil { return fmt.Errorf("DNS update failed: %w", err) } if reply != nil && reply.Rcode != dns.RcodeSuccess { return fmt.Errorf("DNS update failed: server replied: %s", dns.RcodeToString[reply.Rcode]) } return nil }