New DNS provider PowerDNS (#748)

* Added PowerDNS as dns provider

* Remove unnecessary comments

* Some tests

* Implemented feedback

vendor/github.com/mittwald/go-powerdns/pdnshttp/auth_tls.go

@@ -0,0 +1,55 @@
+package pdnshttp
+
+import (
+	"crypto"
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"net/http"
+)
+
+type TLSClientCertificateAuthenticator struct {
+	CACerts    []*x509.Certificate
+	ClientCert tls.Certificate
+	ClientKey  crypto.PrivateKey
+}
+
+func (a *TLSClientCertificateAuthenticator) OnRequest(r *http.Request) error {
+	return nil
+}
+
+func (a *TLSClientCertificateAuthenticator) OnConnect(c *http.Client) error {
+	if c.Transport == nil {
+		c.Transport = http.DefaultTransport
+	}
+
+	t, ok := c.Transport.(*http.Transport)
+	if !ok {
+		return fmt.Errorf("client.Transport is no *http.Transport, instead %t", c.Transport)
+	}
+
+	if t.TLSClientConfig == nil {
+		t.TLSClientConfig = &tls.Config{}
+	}
+
+	if t.TLSClientConfig.Certificates == nil {
+		t.TLSClientConfig.Certificates = make([]tls.Certificate, 0, 1)
+	}
+
+	t.TLSClientConfig.Certificates = append(t.TLSClientConfig.Certificates, a.ClientCert)
+
+	if t.TLSClientConfig.RootCAs == nil {
+		systemPool, err := x509.SystemCertPool()
+		if err != nil {
+			return err
+		}
+
+		t.TLSClientConfig.RootCAs = systemPool
+	}
+
+	for i := range a.CACerts {
+		t.TLSClientConfig.RootCAs.AddCert(a.CACerts[i])
+	}
+
+	return nil
+}