Add client cert authentication

cmd/kube-apiserver/app/server.go

@@ -60,6 +60,7 @@ type APIServer struct {
 	CloudProvider              string
 	CloudConfigFile            string
 	EventTTL                   time.Duration
+	ClientCAFile               string
 	TokenAuthFile              string
 	AuthorizationMode          string
 	AuthorizationPolicyFile    string
@@ -139,6 +140,7 @@ func (s *APIServer) AddFlags(fs *pflag.FlagSet) {
 	fs.StringVar(&s.CloudProvider, "cloud_provider", s.CloudProvider, "The provider for cloud services.  Empty string for no provider.")
 	fs.StringVar(&s.CloudConfigFile, "cloud_config", s.CloudConfigFile, "The path to the cloud provider configuration file.  Empty string for no configuration file.")
 	fs.DurationVar(&s.EventTTL, "event_ttl", s.EventTTL, "Amount of time to retain events. Default 1 hour.")
+	fs.StringVar(&s.ClientCAFile, "client_ca_file", s.ClientCAFile, "If set, any request presenting a client certificate signed by one of the authorities in the client_ca_file is authenticated with an identity corresponding to the CommonName of the client certificate.")
 	fs.StringVar(&s.TokenAuthFile, "token_auth_file", s.TokenAuthFile, "If set, the file that will be used to secure the secure port of the API server via token authentication.")
 	fs.StringVar(&s.AuthorizationMode, "authorization_mode", s.AuthorizationMode, "Selects how to do authorization on the secure port.  One of: "+strings.Join(apiserver.AuthorizationModeChoices, ","))
 	fs.StringVar(&s.AuthorizationPolicyFile, "authorization_policy_file", s.AuthorizationPolicyFile, "File with authorization policy in csv format, used with --authorization_mode=ABAC, on the secure port.")
@@ -222,7 +224,7 @@ func (s *APIServer) Run(_ []string) error {
 
 	n := net.IPNet(s.PortalNet)
 
-	authenticator, err := apiserver.NewAuthenticatorFromTokenFile(s.TokenAuthFile)
+	authenticator, err := apiserver.NewAuthenticator(s.ClientCAFile, s.TokenAuthFile)
 	if err != nil {
 		glog.Fatalf("Invalid Authentication Config: %v", err)
 	}
@@ -330,11 +332,21 @@ func (s *APIServer) Run(_ []string) error {
 			TLSConfig: &tls.Config{
 				// Change default from SSLv3 to TLSv1.0 (because of POODLE vulnerability)
 				MinVersion: tls.VersionTLS10,
-				// Populate PeerCertificates in requests, but don't reject connections without certificates
-				// This allows certificates to be validated by authenticators, while still allowing other auth types
-				ClientAuth: tls.RequestClientCert,
 			},
 		}
+
+		if len(s.ClientCAFile) > 0 {
+			clientCAs, err := util.CertPoolFromFile(s.ClientCAFile)
+			if err != nil {
+				glog.Fatalf("unable to load client CA file: %v", err)
+			}
+			// Populate PeerCertificates in requests, but don't reject connections without certificates
+			// This allows certificates to be validated by authenticators, while still allowing other auth types
+			secureServer.TLSConfig.ClientAuth = tls.RequestClientCert
+			// Specify allowed CAs for client certificates
+			secureServer.TLSConfig.ClientCAs = clientCAs
+		}
+
 		glog.Infof("Serving securely on %s", secureLocation)
 		go func() {
 			defer util.HandleCrash()

docs/authentication.md

@@ -1,8 +1,14 @@
 # Authentication Plugins
 
-Kubernetes uses tokens to authenticate users for API calls.
+Kubernetes uses tokens or client certificates to authenticate users for API calls.
 
-Authentication is enabled by passing the `--token_auth_file=SOMEFILE` option
+Client certificate authentication is enabled by passing the `--client_ca_file=SOMEFILE`
+option to apiserver. The referenced file must contain one or more certificates authorities
+to use to validate client certificates presented to the apiserver. If a client certificate
+is presented and verified, the common name of the subject is used as the user name for the
+request.
+
+Token authentication is enabled by passing the `--token_auth_file=SOMEFILE` option
 to apiserver.  Currently, tokens last indefinitely, and the token list cannot
 be changed without restarting apiserver.  We plan in the future for tokens to
 be short-lived, and to be generated as needed rather than stored in a file.

pkg/apiserver/authn.go

@@ -19,18 +19,61 @@ package apiserver
 import (
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/auth/authenticator"
 	"github.com/GoogleCloudPlatform/kubernetes/pkg/auth/authenticator/bearertoken"
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/util"
+	"github.com/GoogleCloudPlatform/kubernetes/plugin/pkg/auth/authenticator/request/union"
+	"github.com/GoogleCloudPlatform/kubernetes/plugin/pkg/auth/authenticator/request/x509"
 	"github.com/GoogleCloudPlatform/kubernetes/plugin/pkg/auth/authenticator/token/tokenfile"
 )
 
-// NewAuthenticatorFromTokenFile returns an authenticator.Request or an error
-func NewAuthenticatorFromTokenFile(tokenAuthFile string) (authenticator.Request, error) {
-	var authenticator authenticator.Request
-	if len(tokenAuthFile) != 0 {
-		tokenAuthenticator, err := tokenfile.NewCSV(tokenAuthFile)
+// NewAuthenticator returns an authenticator.Request or an error
+func NewAuthenticator(clientCAFile string, tokenFile string) (authenticator.Request, error) {
+	authenticators := []authenticator.Request{}
+
+	if len(clientCAFile) > 0 {
+		certAuth, err := newAuthenticatorFromClientCAFile(clientCAFile)
+		if err != nil {
+			return nil, err
+		}
+		authenticators = append(authenticators, certAuth)
+	}
+
+	if len(tokenFile) > 0 {
+		tokenAuth, err := newAuthenticatorFromTokenFile(tokenFile)
 		if err != nil {
 			return nil, err
 		}
-		authenticator = bearertoken.New(tokenAuthenticator)
+		authenticators = append(authenticators, tokenAuth)
+	}
+
+	if len(authenticators) == 0 {
+		return nil, nil
 	}
-	return authenticator, nil
+	if len(authenticators) == 1 {
+		return authenticators[1], nil
+	}
+	return union.New(authenticators...), nil
+
+}
+
+// newAuthenticatorFromTokenFile returns an authenticator.Request or an error
+func newAuthenticatorFromTokenFile(tokenAuthFile string) (authenticator.Request, error) {
+	tokenAuthenticator, err := tokenfile.NewCSV(tokenAuthFile)
+	if err != nil {
+		return nil, err
+	}
+
+	return bearertoken.New(tokenAuthenticator), nil
+}
+
+// newAuthenticatorFromClientCAFile returns an authenticator.Request or an error
+func newAuthenticatorFromClientCAFile(clientCAFile string) (authenticator.Request, error) {
+	roots, err := util.CertPoolFromFile(clientCAFile)
+	if err != nil {
+		return nil, err
+	}
+
+	opts := x509.DefaultVerifyOptions()
+	opts.Roots = roots
+
+	return x509.New(opts, x509.CommonNameUserConversion), nil
 }

pkg/util/crypto.go

@@ -23,6 +23,7 @@ import (
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/pem"
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"math/big"
@@ -97,3 +98,65 @@ func GenerateSelfSignedCert(host, certPath, keyPath string) error {
 
 	return nil
 }
+
+// CertPoolFromFile returns an x509.CertPool containing the certificates in the given PEM-encoded file.
+// Returns an error if the file could not be read, a certificate could not be parsed, or if the file does not contain any certificates
+func CertPoolFromFile(filename string) (*x509.CertPool, error) {
+	certs, err := certificatesFromFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	pool := x509.NewCertPool()
+	for _, cert := range certs {
+		pool.AddCert(cert)
+	}
+	return pool, nil
+}
+
+// certificatesFromFile returns the x509.Certificates contained in the given PEM-encoded file.
+// Returns an error if the file could not be read, a certificate could not be parsed, or if the file does not contain any certificates
+func certificatesFromFile(file string) ([]*x509.Certificate, error) {
+	if len(file) == 0 {
+		return nil, errors.New("error reading certificates from an empty filename")
+	}
+	pemBlock, err := ioutil.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+	certs, err := certsFromPEM(pemBlock)
+	if err != nil {
+		return nil, fmt.Errorf("error reading %s: %s", file, err)
+	}
+	return certs, nil
+}
+
+// certsFromPEM returns the x509.Certificates contained in the given PEM-encoded byte array
+// Returns an error if a certificate could not be parsed, or if the data does not contain any certificates
+func certsFromPEM(pemCerts []byte) ([]*x509.Certificate, error) {
+	ok := false
+	certs := []*x509.Certificate{}
+	for len(pemCerts) > 0 {
+		var block *pem.Block
+		block, pemCerts = pem.Decode(pemCerts)
+		if block == nil {
+			break
+		}
+		// Only use PEM "CERTIFICATE" blocks without extra headers
+		if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
+			continue
+		}
+
+		cert, err := x509.ParseCertificate(block.Bytes)
+		if err != nil {
+			return certs, err
+		}
+
+		certs = append(certs, cert)
+		ok = true
+	}
+
+	if !ok {
+		return certs, errors.New("could not read any certificates")
+	}
+	return certs, nil
+}