Cache loopback cert in the certs dir if set

staging/src/k8s.io/apiserver/pkg/server/options/serving_with_loopback.go

@@ -51,7 +51,7 @@ func (s *SecureServingOptionsWithLoopback) ApplyTo(secureServingInfo **server.Se
 
 	// create self-signed cert+key with the fake server.LoopbackClientServerNameOverride and
 	// let the server return it when the loopback client connects.
-	certPem, keyPem, err := certutil.GenerateSelfSignedCertKey(server.LoopbackClientServerNameOverride, nil, nil)
+	certPem, keyPem, err := certutil.GenerateSelfSignedCertKeyWithFixtures(server.LoopbackClientServerNameOverride, nil, nil, s.SecureServingOptions.ServerCert.CertDirectory)
 	if err != nil {
 		return fmt.Errorf("failed to generate self-signed certificate for loopback connection: %v", err)
 	}