create utilities inspecting server TLS certs

Kubernetes-commit: e44352f31a8d506d77d2757dbb354fd539826c92

util/cert/server_inspection.go

@@ -0,0 +1,97 @@
+/*
+Copyright 2019 The Kubernetes 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 cert
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"net/url"
+	"strings"
+)
+
+// GetClientCANames gets the CA names for client certs that a server accepts.  This is useful when inspecting the
+// state of particular servers.  apiHost is "host:port"
+func GetClientCANames(apiHost string) ([]string, error) {
+	// when we run this the second time, we know which one we are expecting
+	acceptableCAs := []string{}
+	tlsConfig := &tls.Config{
+		InsecureSkipVerify: true, // this is insecure to always get to the GetClientCertificate
+		GetClientCertificate: func(hello *tls.CertificateRequestInfo) (*tls.Certificate, error) {
+			acceptableCAs = []string{}
+			for _, curr := range hello.AcceptableCAs {
+				acceptableCAs = append(acceptableCAs, string(curr))
+			}
+			return &tls.Certificate{}, nil
+		},
+	}
+
+	conn, err := tls.Dial("tcp", apiHost, tlsConfig)
+	if err != nil {
+		return nil, err
+	}
+	defer conn.Close()
+
+	return acceptableCAs, nil
+}
+
+// GetClientCANamesForURL is GetClientCANames against a URL string like we use in kubeconfigs
+func GetClientCANamesForURL(kubeConfigURL string) ([]string, error) {
+	apiserverURL, err := url.Parse(kubeConfigURL)
+	if err != nil {
+		return nil, err
+	}
+	return GetClientCANames(apiserverURL.Host)
+}
+
+// GetServingCertificates returns the x509 certs used by a server.  The serverName is optional for specifying a different
+// name to get SNI certificates.  apiHost is "host:port"
+func GetServingCertificates(apiHost, serverName string) ([]*x509.Certificate, [][]byte, error) {
+	tlsConfig := &tls.Config{
+		InsecureSkipVerify: true, // this is insecure so that we always get connected
+	}
+	// if a name is specified for SNI, set it.
+	if len(serverName) > 0 {
+		tlsConfig.ServerName = serverName
+	}
+
+	conn, err := tls.Dial("tcp", apiHost, tlsConfig)
+	if err != nil {
+		return nil, nil, err
+	}
+	conn.Close()
+
+	peerCerts := conn.ConnectionState().PeerCertificates
+	peerCertBytes := [][]byte{}
+	for _, a := range peerCerts {
+		actualCert, err := EncodeCertificates(a)
+		if err != nil {
+			return nil, nil, err
+		}
+		peerCertBytes = append(peerCertBytes, []byte(strings.TrimSpace(string(actualCert))))
+	}
+
+	return peerCerts, peerCertBytes, err
+}
+
+// GetServingCertificatesForURL is GetServingCertificates against a URL string like we use in kubeconfigs
+func GetServingCertificatesForURL(kubeConfigURL, serverName string) ([]*x509.Certificate, [][]byte, error) {
+	apiserverURL, err := url.Parse(kubeConfigURL)
+	if err != nil {
+		return nil, nil, err
+	}
+	return GetServingCertificates(apiserverURL.Host, serverName)
+}