caddytls: Finish upgrading to libdns DNS providers for ACME challenges

Until we finish the migration to the new acme library, we have to bring
the solver type in-house. It's small and temporary.

modules/caddytls/acmeissuer.go

@@ -91,7 +91,21 @@ func (m *ACMEIssuer) Provision(ctx caddy.Context) error {
 		if err != nil {
 			return fmt.Errorf("loading DNS provider module: %v", err)
 		}
-		m.Challenges.DNS.provider = val.(challenge.Provider)
+		// TODO: For a temporary amount of time, we are allowing the use of
+		// DNS providers from go-acme/lego since there are so many implemented
+		// for it -- they are adapted as Caddy modules in this repository:
+		// https://github.com/caddy-dns/lego-deprecated - that module is
+		// a challenge.Provider value, so we use it directly. The user must set
+		// environment variables to configure it. Remove this shim once a sufficient
+		// number of DNS providers are implemented for the libdns APIs instead.
+		if grandfatheredProvider, ok := val.(challenge.Provider); ok {
+			m.Challenges.DNS.provider = grandfatheredProvider
+		} else {
+			m.Challenges.DNS.provider = &solver{
+				recordManager: val.(recordManager),
+				TTL:           time.Duration(m.Challenges.DNS.TTL),
+			}
+		}
 	}
 
 	// add any custom CAs to trust store

modules/caddytls/dnssolver.go

@@ -0,0 +1,113 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package caddytls
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/go-acme/lego/v3/challenge"
+	"github.com/go-acme/lego/v3/challenge/dns01"
+	"github.com/libdns/libdns"
+)
+
+// TODO: this is borrowed from https://github.com/mholt/acme - once we
+// switch to that acme library, this file will go away
+
+// solver is a type that makes libdns providers usable as ACME challenge solvers.
+type solver struct {
+	recordManager
+
+	TTL time.Duration
+
+	txtRecords   map[string]libdns.Record // keyed by challenge token
+	txtRecordsMu sync.Mutex
+}
+
+func (s *solver) Present(domain, token, keyAuth string) error {
+	fqdn, value := dns01.GetRecord(domain, keyAuth)
+
+	rec := libdns.Record{
+		Type:  "TXT",
+		Name:  fqdn,
+		Value: value,
+		TTL:   s.TTL,
+	}
+
+	zone, err := dns01.FindZoneByFqdn(fqdn)
+	if err != nil {
+		return fmt.Errorf("could not determine zone for domain %q: %v", fqdn, err)
+	}
+
+	results, err := s.recordManager.AppendRecords(context.TODO(), zone, []libdns.Record{rec})
+	if err != nil {
+		return err
+	}
+	if len(results) != 1 {
+		return fmt.Errorf("expected one record, got %d: %v", len(results), results)
+	}
+
+	// keep this record handy so we can clean it up more efficiently
+	s.txtRecordsMu.Lock()
+	if s.txtRecords == nil {
+		s.txtRecords = make(map[string]libdns.Record)
+	}
+	s.txtRecords[keyAuth] = results[0]
+	s.txtRecordsMu.Unlock()
+
+	// TODO: check for record propagation before continuing (accordig to config)
+
+	return nil
+}
+
+func (s *solver) CleanUp(domain, token, keyAuth string) error {
+	fqdn, _ := dns01.GetRecord(domain, keyAuth)
+	authZone, err := dns01.FindZoneByFqdn(fqdn)
+	if err != nil {
+		return err
+	}
+
+	// retrieve the record we created
+	s.txtRecordsMu.Lock()
+	txtRec, ok := s.txtRecords[keyAuth]
+	if !ok {
+		s.txtRecordsMu.Unlock()
+		return fmt.Errorf("no memory of presenting a DNS record for %v", domain)
+	}
+	s.txtRecordsMu.Unlock()
+
+	// clean up the record
+	_, err = s.recordManager.DeleteRecords(context.TODO(), authZone, []libdns.Record{txtRec})
+	if err != nil {
+		return err
+	}
+
+	// once it has been successfully cleaned up, we can forget about it
+	s.txtRecordsMu.Lock()
+	delete(s.txtRecords, keyAuth)
+	s.txtRecordsMu.Unlock()
+
+	return nil
+}
+
+// recordManager defines the set of operations required for ACME challenges.
+type recordManager interface {
+	libdns.RecordAppender
+	libdns.RecordDeleter
+}
+
+var _ challenge.Provider = (*solver)(nil)