lego/acme/dns_challenge_rfc2136.go

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package acme
import (
"fmt"
"strings"
"time"
"github.com/miekg/dns"
)
// DNSProviderRFC2136 is an implementation of the ChallengeProvider interface that
// uses dynamic DNS updates (RFC 2136) to create TXT records on a nameserver.
type DNSProviderRFC2136 struct {
nameserver string
tsigAlgorithm string
tsigKey string
tsigSecret string
domain2zone map[string]string
}
// NewDNSProviderRFC2136 returns a new DNSProviderRFC2136 instance.
// To disable TSIG authentication 'tsigAlgorithm, 'tsigKey' and 'tsigSecret' must be set to the empty string.
// 'nameserver' must be a network address in the the form "host" or "host:port".
func NewDNSProviderRFC2136(nameserver, tsigAlgorithm, tsigKey, tsigSecret string) (*DNSProviderRFC2136, error) {
// Append the default DNS port if none is specified.
if !strings.Contains(nameserver, ":") {
nameserver += ":53"
}
d := &DNSProviderRFC2136{
nameserver: nameserver,
domain2zone: make(map[string]string),
}
if tsigAlgorithm == "" {
tsigAlgorithm = dns.HmacMD5
}
d.tsigAlgorithm = tsigAlgorithm
if len(tsigKey) > 0 && len(tsigSecret) > 0 {
d.tsigKey = tsigKey
d.tsigSecret = tsigSecret
}
return d, nil
}
// Present creates a TXT record using the specified parameters
func (r *DNSProviderRFC2136) Present(domain, token, keyAuth string) error {
fqdn, value, ttl := DNS01Record(domain, keyAuth)
return r.changeRecord("INSERT", fqdn, value, ttl)
}
// CleanUp removes the TXT record matching the specified parameters
func (r *DNSProviderRFC2136) CleanUp(domain, token, keyAuth string) error {
fqdn, value, ttl := DNS01Record(domain, keyAuth)
return r.changeRecord("REMOVE", fqdn, value, ttl)
}
func (r *DNSProviderRFC2136) changeRecord(action, fqdn, value string, ttl int) error {
zone, err := r.findZone(fqdn)
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 := make([]dns.RR, 1)
rrs[0] = 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 := new(dns.Client)
c.SingleInflight = true
// TSIG authentication / msg signing
if len(r.tsigKey) > 0 && len(r.tsigSecret) > 0 {
m.SetTsig(dns.Fqdn(r.tsigKey), r.tsigAlgorithm, 300, time.Now().Unix())
c.TsigSecret = map[string]string{dns.Fqdn(r.tsigKey): r.tsigSecret}
}
// Send the query
reply, _, err := c.Exchange(m, r.nameserver)
if err != nil {
return fmt.Errorf("DNS update failed: %v", err)
}
if reply != nil && reply.Rcode != dns.RcodeSuccess {
return fmt.Errorf("DNS update failed. Server replied: %s", dns.RcodeToString[reply.Rcode])
}
return nil
}
// findZone determines the zone of a qualifying cert DNSname
func (r *DNSProviderRFC2136) findZone(fqdn string) (string, error) {
// Do we have it cached?
if val, ok := r.domain2zone[fqdn]; ok {
return val, nil
}
// Query the authorative nameserver for a hopefully non-existing SOA record,
// in the authority section of the reply it will have the SOA of the
// containing zone. rfc2308 has this to say on the subject:
// Name servers authoritative for a zone MUST include the SOA record of
// the zone in the authority section of the response when reporting an
// NXDOMAIN or indicating that no data (NODATA) of the requested type exists
m := new(dns.Msg)
m.SetQuestion(fqdn, dns.TypeSOA)
m.SetEdns0(4096, false)
m.RecursionDesired = true
m.Authoritative = true
in, err := dns.Exchange(m, r.nameserver)
if err == dns.ErrTruncated {
tcp := &dns.Client{Net: "tcp"}
in, _, err = tcp.Exchange(m, r.nameserver)
}
if err != nil {
return "", err
}
if in.Rcode != dns.RcodeNameError {
if in.Rcode != dns.RcodeSuccess {
return "", fmt.Errorf("DNS Query for zone %q failed", fqdn)
}
// We have a success, so one of the answers has to be a SOA RR
for _, ans := range in.Answer {
if ans.Header().Rrtype == dns.TypeSOA {
zone := ans.Header().Name
r.domain2zone[fqdn] = zone
return zone, nil
}
}
// Or it is NODATA, fall through to NXDOMAIN
}
// Search the authority section for our precious SOA RR
for _, ns := range in.Ns {
if ns.Header().Rrtype == dns.TypeSOA {
zone := ns.Header().Name
r.domain2zone[fqdn] = zone
return zone, nil
}
}
return "", fmt.Errorf("Expected a SOA record in the authority section")
}