oidc authentication: switch to v2 of coreos/go-oidc

cmd/kube-apiserver/app/options/options_test.go

@@ -210,6 +210,7 @@ func TestAddFlags(t *testing.T) {
 			BootstrapToken: &kubeoptions.BootstrapTokenAuthenticationOptions{},
 			OIDC: &kubeoptions.OIDCAuthenticationOptions{
 				UsernameClaim: "sub",
+				SigningAlgs:   []string{"RS256"},
 			},
 			PasswordFile:  &kubeoptions.PasswordFileAuthenticationOptions{},
 			RequestHeader: &apiserveroptions.RequestHeaderAuthenticationOptions{},

pkg/kubeapiserver/authenticator/config.go

@@ -58,6 +58,7 @@ type AuthenticatorConfig struct {
 	OIDCUsernamePrefix          string
 	OIDCGroupsClaim             string
 	OIDCGroupsPrefix            string
+	OIDCSigningAlgs             []string
 	ServiceAccountKeyFiles      []string
 	ServiceAccountLookup        bool
 	WebhookTokenAuthnConfigFile string
@@ -143,7 +144,7 @@ func (config AuthenticatorConfig) New() (authenticator.Request, *spec.SecurityDe
 	// simply returns an error, the OpenID Connect plugin may query the provider to
 	// update the keys, causing performance hits.
 	if len(config.OIDCIssuerURL) > 0 && len(config.OIDCClientID) > 0 {
-		oidcAuth, err := newAuthenticatorFromOIDCIssuerURL(config.OIDCIssuerURL, config.OIDCClientID, config.OIDCCAFile, config.OIDCUsernameClaim, config.OIDCUsernamePrefix, config.OIDCGroupsClaim, config.OIDCGroupsPrefix)
+		oidcAuth, err := newAuthenticatorFromOIDCIssuerURL(config.OIDCIssuerURL, config.OIDCClientID, config.OIDCCAFile, config.OIDCUsernameClaim, config.OIDCUsernamePrefix, config.OIDCGroupsClaim, config.OIDCGroupsPrefix, config.OIDCSigningAlgs)
 		if err != nil {
 			return nil, nil, err
 		}
@@ -235,7 +236,7 @@ func newAuthenticatorFromTokenFile(tokenAuthFile string) (authenticator.Token, e
 }
 
 // newAuthenticatorFromOIDCIssuerURL returns an authenticator.Token or an error.
-func newAuthenticatorFromOIDCIssuerURL(issuerURL, clientID, caFile, usernameClaim, usernamePrefix, groupsClaim, groupsPrefix string) (authenticator.Token, error) {
+func newAuthenticatorFromOIDCIssuerURL(issuerURL, clientID, caFile, usernameClaim, usernamePrefix, groupsClaim, groupsPrefix string, signingAlgs []string) (authenticator.Token, error) {
 	const noUsernamePrefix = "-"
 
 	if usernamePrefix == "" && usernameClaim != "email" {
@@ -251,14 +252,15 @@ func newAuthenticatorFromOIDCIssuerURL(issuerURL, clientID, caFile, usernameClai
 		usernamePrefix = ""
 	}
 
-	tokenAuthenticator, err := oidc.New(oidc.OIDCOptions{
-		IssuerURL:      issuerURL,
-		ClientID:       clientID,
-		CAFile:         caFile,
-		UsernameClaim:  usernameClaim,
-		UsernamePrefix: usernamePrefix,
-		GroupsClaim:    groupsClaim,
-		GroupsPrefix:   groupsPrefix,
+	tokenAuthenticator, err := oidc.New(oidc.Options{
+		IssuerURL:            issuerURL,
+		ClientID:             clientID,
+		CAFile:               caFile,
+		UsernameClaim:        usernameClaim,
+		UsernamePrefix:       usernamePrefix,
+		GroupsClaim:          groupsClaim,
+		GroupsPrefix:         groupsPrefix,
+		SupportedSigningAlgs: signingAlgs,
 	})
 	if err != nil {
 		return nil, err

pkg/kubeapiserver/options/authentication.go

@@ -61,6 +61,7 @@ type OIDCAuthenticationOptions struct {
 	UsernamePrefix string
 	GroupsClaim    string
 	GroupsPrefix   string
+	SigningAlgs    []string
 }
 
 type PasswordFileAuthenticationOptions struct {
@@ -208,6 +209,10 @@ func (s *BuiltInAuthenticationOptions) AddFlags(fs *pflag.FlagSet) {
 			"If provided, all groups will be prefixed with this value to prevent conflicts with "+
 			"other authentication strategies.")
 
+		fs.StringSliceVar(&s.OIDC.SigningAlgs, "oidc-signing-algs", []string{"RS256"}, ""+
+			"Comma-separated list of allowed JOSE asymmetric signing algorithms. JWTs with a "+
+			"'alg' header value not in this list will be rejected. "+
+			"Values are defined by RFC 7518 https://tools.ietf.org/html/rfc7518#section-3.1.")
 	}
 
 	if s.PasswordFile != nil {
@@ -272,6 +277,7 @@ func (s *BuiltInAuthenticationOptions) ToAuthenticationConfig() authenticator.Au
 		ret.OIDCIssuerURL = s.OIDC.IssuerURL
 		ret.OIDCUsernameClaim = s.OIDC.UsernameClaim
 		ret.OIDCUsernamePrefix = s.OIDC.UsernamePrefix
+		ret.OIDCSigningAlgs = s.OIDC.SigningAlgs
 	}
 
 	if s.PasswordFile != nil {

staging/src/k8s.io/apiserver/plugin/pkg/authenticator/token/oidc/oidc.go

@@ -17,7 +17,7 @@ limitations under the License.
 /*
 oidc implements the authenticator.Token interface using the OpenID Connect protocol.
 
-	config := oidc.OIDCOptions{
+	config := oidc.Options{
 		IssuerURL:     "https://accounts.google.com",
 		ClientID:      os.Getenv("GOOGLE_CLIENT_ID"),
 		UsernameClaim: "email",
@@ -27,25 +27,28 @@ oidc implements the authenticator.Token interface using the OpenID Connect proto
 package oidc
 
 import (
+	"context"
 	"crypto/tls"
 	"crypto/x509"
+	"encoding/base64"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
-	"sync"
+	"strings"
 	"sync/atomic"
+	"time"
 
-	"github.com/coreos/go-oidc/jose"
-	"github.com/coreos/go-oidc/oidc"
+	oidc "github.com/coreos/go-oidc"
 	"github.com/golang/glog"
 	"k8s.io/apimachinery/pkg/util/net"
-	"k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/apiserver/pkg/authentication/user"
 	certutil "k8s.io/client-go/util/cert"
 )
 
-type OIDCOptions struct {
+type Options struct {
 	// IssuerURL is the URL the provider signs ID Tokens as. This will be the "iss"
 	// field of all tokens produced by the provider and is used for configuration
 	// discovery.
@@ -83,30 +86,85 @@ type OIDCOptions struct {
 	// GroupsPrefix, if specified, causes claims mapping to group names to be prefixed with the
 	// value. A value "oidc:" would result in groups like "oidc:engineering" and "oidc:marketing".
 	GroupsPrefix string
+
+	// SupportedSigningAlgs sets the accepted set of JOSE signing algorithms that
+	// can be used by the provider to sign tokens.
+	//
+	// https://tools.ietf.org/html/rfc7518#section-3.1
+	//
+	// This value defaults to RS256, the value recommended by the OpenID Connect
+	// spec:
+	//
+	// https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation
+	SupportedSigningAlgs []string
+
+	// now is used for testing. It defaults to time.Now.
+	now func() time.Time
 }
 
-type OIDCAuthenticator struct {
+type Authenticator struct {
 	issuerURL string
 
-	trustedClientID string
-
 	usernameClaim  string
 	usernamePrefix string
 	groupsClaim    string
 	groupsPrefix   string
 
-	httpClient *http.Client
+	// Contains an *oidc.IDTokenVerifier. Do not access directly use the
+	// idTokenVerifier method.
+	verifier atomic.Value
 
-	// Contains an *oidc.Client. Do not access directly. Use client() method.
-	oidcClient atomic.Value
-
-	// Guards the close method and is used to lock during initialization and closing.
-	mu    sync.Mutex
-	close func() // May be nil
+	cancel context.CancelFunc
 }
 
-// New creates a token authenticator which validates OpenID Connect ID Tokens.
-func New(opts OIDCOptions) (*OIDCAuthenticator, error) {
+func (a *Authenticator) setVerifier(v *oidc.IDTokenVerifier) {
+	a.verifier.Store(v)
+}
+
+func (a *Authenticator) idTokenVerifier() (*oidc.IDTokenVerifier, bool) {
+	if v := a.verifier.Load(); v != nil {
+		return v.(*oidc.IDTokenVerifier), true
+	}
+	return nil, false
+}
+
+func (a *Authenticator) Close() {
+	a.cancel()
+}
+
+func New(opts Options) (*Authenticator, error) {
+	return newAuthenticator(opts, func(ctx context.Context, a *Authenticator, config *oidc.Config) {
+		// Asynchronously attempt to initialize the authenticator. This enables
+		// self-hosted providers, providers that run on top of Kubernetes itself.
+		go wait.PollUntil(time.Second*10, func() (done bool, err error) {
+			provider, err := oidc.NewProvider(ctx, a.issuerURL)
+			if err != nil {
+				glog.Errorf("oidc authenticator: initializing plugin: %v", err)
+				return false, nil
+			}
+
+			verifier := provider.Verifier(config)
+			a.setVerifier(verifier)
+			return true, nil
+		}, ctx.Done())
+	})
+}
+
+// whitelist of signing algorithms to ensure users don't mistakenly pass something
+// goofy.
+var allowedSigningAlgs = map[string]bool{
+	oidc.RS256: true,
+	oidc.RS384: true,
+	oidc.RS512: true,
+	oidc.ES256: true,
+	oidc.ES384: true,
+	oidc.ES512: true,
+	oidc.PS256: true,
+	oidc.PS384: true,
+	oidc.PS512: true,
+}
+
+func newAuthenticator(opts Options, initVerifier func(ctx context.Context, a *Authenticator, config *oidc.Config)) (*Authenticator, error) {
 	url, err := url.Parse(opts.IssuerURL)
 	if err != nil {
 		return nil, err
@@ -120,6 +178,18 @@ func New(opts OIDCOptions) (*OIDCAuthenticator, error) {
 		return nil, errors.New("no username claim provided")
 	}
 
+	supportedSigningAlgs := opts.SupportedSigningAlgs
+	if len(supportedSigningAlgs) == 0 {
+		// RS256 is the default recommended by OpenID Connect and an 'alg' value
+		// providers are required to implement.
+		supportedSigningAlgs = []string{oidc.RS256}
+	}
+	for _, alg := range supportedSigningAlgs {
+		if !allowedSigningAlgs[alg] {
+			return nil, fmt.Errorf("oidc: unsupported signing alg: %q", alg)
+		}
+	}
+
 	var roots *x509.CertPool
 	if opts.CAFile != "" {
 		roots, err = certutil.NewPool(opts.CAFile)
@@ -137,137 +207,91 @@ func New(opts OIDCOptions) (*OIDCAuthenticator, error) {
 		TLSClientConfig: &tls.Config{RootCAs: roots},
 	})
 
-	authenticator := &OIDCAuthenticator{
-		issuerURL:       opts.IssuerURL,
-		trustedClientID: opts.ClientID,
-		usernameClaim:   opts.UsernameClaim,
-		usernamePrefix:  opts.UsernamePrefix,
-		groupsClaim:     opts.GroupsClaim,
-		groupsPrefix:    opts.GroupsPrefix,
-		httpClient:      &http.Client{Transport: tr},
+	client := &http.Client{Transport: tr, Timeout: 30 * time.Second}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	ctx = oidc.ClientContext(ctx, client)
+
+	authenticator := &Authenticator{
+		issuerURL:      opts.IssuerURL,
+		usernameClaim:  opts.UsernameClaim,
+		usernamePrefix: opts.UsernamePrefix,
+		groupsClaim:    opts.GroupsClaim,
+		groupsPrefix:   opts.GroupsPrefix,
+		cancel:         cancel,
 	}
 
-	// Attempt to initialize the authenticator asynchronously.
-	//
-	// Ignore errors instead of returning it since the OpenID Connect provider might not be
-	// available yet, for instance if it's running on the cluster and needs the API server
-	// to come up first. Errors will be logged within the client() method.
-	go func() {
-		defer runtime.HandleCrash()
-		authenticator.client()
-	}()
+	now := opts.now
+	if now == nil {
+		now = time.Now
+	}
 
+	verifierConfig := &oidc.Config{
+		ClientID:             opts.ClientID,
+		SupportedSigningAlgs: supportedSigningAlgs,
+		Now:                  now,
+	}
+
+	initVerifier(ctx, authenticator, verifierConfig)
 	return authenticator, nil
 }
 
-// Close stops all goroutines used by the authenticator.
-func (a *OIDCAuthenticator) Close() {
-	a.mu.Lock()
-	defer a.mu.Unlock()
-
-	if a.close != nil {
-		a.close()
+func hasCorrectIssuer(iss, tokenData string) bool {
+	parts := strings.Split(tokenData, ".")
+	if len(parts) != 3 {
+		return false
 	}
-	return
+	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
+	if err != nil {
+		return false
+	}
+	claims := struct {
+		// WARNING: this JWT is not verified. Do not trust these claims.
+		Issuer string `json:"iss"`
+	}{}
+	if err := json.Unmarshal(payload, &claims); err != nil {
+		return false
+	}
+	if claims.Issuer != iss {
+		return false
+	}
+	return true
 }
 
-func (a *OIDCAuthenticator) client() (*oidc.Client, error) {
-	// Fast check to see if client has already been initialized.
-	if client := a.oidcClient.Load(); client != nil {
-		return client.(*oidc.Client), nil
+func (a *Authenticator) AuthenticateToken(token string) (user.Info, bool, error) {
+	if !hasCorrectIssuer(a.issuerURL, token) {
+		return nil, false, nil
 	}
 
-	// Acquire lock, then recheck initialization.
-	a.mu.Lock()
-	defer a.mu.Unlock()
-	if client := a.oidcClient.Load(); client != nil {
-		return client.(*oidc.Client), nil
-	}
-
-	// Try to initialize client.
-	providerConfig, err := oidc.FetchProviderConfig(a.httpClient, a.issuerURL)
-	if err != nil {
-		glog.Errorf("oidc authenticator: failed to fetch provider discovery data: %v", err)
-		return nil, fmt.Errorf("fetch provider config: %v", err)
-	}
-
-	clientConfig := oidc.ClientConfig{
-		HTTPClient:     a.httpClient,
-		Credentials:    oidc.ClientCredentials{ID: a.trustedClientID},
-		ProviderConfig: providerConfig,
-	}
-
-	client, err := oidc.NewClient(clientConfig)
-	if err != nil {
-		glog.Errorf("oidc authenticator: failed to create client: %v", err)
-		return nil, fmt.Errorf("create client: %v", err)
-	}
-
-	// SyncProviderConfig will start a goroutine to periodically synchronize the provider config.
-	// The synchronization interval is set by the expiration length of the config, and has a minimum
-	// and maximum threshold.
-	stop := client.SyncProviderConfig(a.issuerURL)
-	a.oidcClient.Store(client)
-	a.close = func() {
-		// This assumes the stop is an unbuffered channel.
-		// So instead of closing the channel, we send am empty struct here.
-		// This guarantees that when this function returns, there is no flying requests,
-		// because a send to an unbuffered channel happens after the receive from the channel.
-		stop <- struct{}{}
-	}
-	return client, nil
-}
-
-// AuthenticateToken decodes and verifies an ID Token using the OIDC client, if the verification succeeds,
-// then it will extract the user info from the JWT claims.
-func (a *OIDCAuthenticator) AuthenticateToken(value string) (user.Info, bool, error) {
-	jwt, err := jose.ParseJWT(value)
-	if err != nil {
-		return nil, false, err
-	}
-
-	client, err := a.client()
-	if err != nil {
-		return nil, false, err
-	}
-	if err := client.VerifyJWT(jwt); err != nil {
-		return nil, false, err
-	}
-	claims, err := jwt.Claims()
-	if err != nil {
-		return nil, false, err
-	}
-	return a.parseTokenClaims(claims)
-}
-
-// parseTokenClaims maps a set of claims to a user. It performs basic validation such as
-// ensuring the email is verified.
-func (a *OIDCAuthenticator) parseTokenClaims(claims jose.Claims) (user.Info, bool, error) {
-	username, ok, err := claims.StringClaim(a.usernameClaim)
-	if err != nil {
-		return nil, false, err
-	}
+	ctx := context.Background()
+	verifier, ok := a.idTokenVerifier()
 	if !ok {
-		return nil, false, fmt.Errorf("cannot find %q in JWT claims", a.usernameClaim)
+		return nil, false, fmt.Errorf("oidc: authenticator not initialized")
+	}
+
+	idToken, err := verifier.Verify(ctx, token)
+	if err != nil {
+		return nil, false, fmt.Errorf("oidc: verify token: %v", err)
+	}
+
+	var c claims
+	if err := idToken.Claims(&c); err != nil {
+		return nil, false, fmt.Errorf("oidc: parse claims: %v", err)
+	}
+	var username string
+	if err := c.unmarshalClaim(a.usernameClaim, &username); err != nil {
+		return nil, false, fmt.Errorf("oidc: parse username claims %q: %v", a.usernameClaim, err)
 	}
 
 	if a.usernameClaim == "email" {
-		verified, ok := claims["email_verified"]
-		if !ok {
-			return nil, false, errors.New("'email_verified' claim not present")
+		// Check the email_verified claim to ensure the email is valid.
+		// https://openid.net/specs/openid-connect-core-1_0.html#StandardClaims
+		var emailVerified bool
+		if err := c.unmarshalClaim("email_verified", &emailVerified); err != nil {
+			return nil, false, fmt.Errorf("oidc: parse 'email_verified' claim: %v", err)
 		}
-
-		emailVerified, ok := verified.(bool)
-		if !ok {
-			// OpenID Connect spec defines 'email_verified' as a boolean. For now, be a pain and error if
-			// it's a different type. If there are enough misbehaving providers we can relax this latter.
-			//
-			// See: https://openid.net/specs/openid-connect-core-1_0.html#StandardClaims
-			return nil, false, fmt.Errorf("malformed claim 'email_verified', expected boolean got %T", verified)
-		}
-
 		if !emailVerified {
-			return nil, false, errors.New("email not verified")
+			return nil, false, fmt.Errorf("oidc: email not verified")
 		}
 	}
 
@@ -275,21 +299,18 @@ func (a *OIDCAuthenticator) parseTokenClaims(claims jose.Claims) (user.Info, boo
 		username = a.usernamePrefix + username
 	}
 
-	// TODO(yifan): Add UID, also populate the issuer to upper layer.
 	info := &user.DefaultInfo{Name: username}
-
 	if a.groupsClaim != "" {
-		groups, found, err := claims.StringsClaim(a.groupsClaim)
-		if err != nil {
-			// Groups type is present but is not an array of strings, try to decode as a string.
-			group, _, err := claims.StringClaim(a.groupsClaim)
-			if err != nil {
-				// Custom claim is present, but isn't an array of strings or a string.
-				return nil, false, fmt.Errorf("custom group claim contains invalid type: %T", claims[a.groupsClaim])
+		if _, ok := c[a.groupsClaim]; ok {
+			// Some admins want to use string claims like "role" as the group value.
+			// Allow the group claim to be a single string instead of an array.
+			//
+			// See: https://github.com/kubernetes/kubernetes/issues/33290
+			var groups stringOrArray
+			if err := c.unmarshalClaim(a.groupsClaim, &groups); err != nil {
+				return nil, false, fmt.Errorf("oidc: parse groups claim %q: %v", a.groupsClaim, err)
 			}
-			info.Groups = []string{group}
-		} else if found {
-			info.Groups = groups
+			info.Groups = []string(groups)
 		}
 	}
 
@@ -298,6 +319,31 @@ func (a *OIDCAuthenticator) parseTokenClaims(claims jose.Claims) (user.Info, boo
 			info.Groups[i] = a.groupsPrefix + group
 		}
 	}
-
 	return info, true, nil
 }
+
+type stringOrArray []string
+
+func (s *stringOrArray) UnmarshalJSON(b []byte) error {
+	var a []string
+	if err := json.Unmarshal(b, &a); err == nil {
+		*s = a
+		return nil
+	}
+	var str string
+	if err := json.Unmarshal(b, &str); err != nil {
+		return err
+	}
+	*s = []string{str}
+	return nil
+}
+
+type claims map[string]json.RawMessage
+
+func (c claims) unmarshalClaim(name string, v interface{}) error {
+	val, ok := c[name]
+	if !ok {
+		return fmt.Errorf("claim not present")
+	}
+	return json.Unmarshal([]byte(val), v)
+}

staging/src/k8s.io/apiserver/plugin/pkg/authenticator/token/oidc/testdata/gen.sh

@@ -0,0 +1,27 @@
+#!/bin/bash -e
+
+# Copyright 2018 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.
+
+rm *.pem
+
+for N in `seq 1 3`; do
+    ssh-keygen -t rsa -b 2048 -f rsa_$N.pem -N ''
+done
+
+for N in `seq 1 3`; do
+    ssh-keygen -t ecdsa -b 521 -f ecdsa_$N.pem -N ''
+done
+
+rm *.pub