pdns: fix wildcard with SANs (#837)

The current implementation of the DNS challenge does not allow
to set multiple TXT records at once.

As PowerDNS has the concept of record sets, and so all records
for the same type and name must set during one call, we would override
existing records.

To avoid this, we merge the new TXT record with existing ones

providers/dns/pdns/client.go

@@ -127,7 +127,7 @@ func (d *DNSProvider) findTxtRecord(fqdn string) (*rrSet, error) {
 		}
 	}
 
-	return nil, fmt.Errorf("no existing record found for %s", fqdn)
+	return nil, nil
 }
 
 func (d *DNSProvider) getAPIVersion() (int, error) {

providers/dns/pdns/pdns.go

@@ -121,6 +121,19 @@ func (d *DNSProvider) Present(domain, token, keyAuth string) error {
 		TTL:  d.config.TTL,
 	}
 
+	// Look for existing records.
+	existingRrSet, err := d.findTxtRecord(fqdn)
+	if err != nil {
+		return fmt.Errorf("pdns: %v", err)
+	}
+
+	// merge the existing and new records
+	var records []Record
+	if existingRrSet != nil {
+		records = existingRrSet.Records
+	}
+	records = append(records, rec)
+
 	rrsets := rrSets{
 		RRSets: []rrSet{
 			{
@@ -129,7 +142,7 @@ func (d *DNSProvider) Present(domain, token, keyAuth string) error {
 				Type:       "TXT",
 				Kind:       "Master",
 				TTL:        d.config.TTL,
-				Records:    []Record{rec},
+				Records:    records,
 			},
 		},
 	}
@@ -159,6 +172,9 @@ func (d *DNSProvider) CleanUp(domain, token, keyAuth string) error {
 	if err != nil {
 		return fmt.Errorf("pdns: %v", err)
 	}
+	if set == nil {
+		return fmt.Errorf("pdns: no existing record found for %s", fqdn)
+	}
 
 	rrsets := rrSets{
 		RRSets: []rrSet{