build source

vendor/k8s.io/client-go/plugin/pkg/client/auth/exec/exec.go

@@ -0,0 +1,702 @@
+/*
+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.
+*/
+
+package exec
+
+import (
+	"bytes"
+	"crypto/tls"
+	"crypto/x509"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"reflect"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/term"
+
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/schema"
+	"k8s.io/apimachinery/pkg/runtime/serializer"
+	"k8s.io/apimachinery/pkg/util/dump"
+	utilnet "k8s.io/apimachinery/pkg/util/net"
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/client-go/pkg/apis/clientauthentication"
+	"k8s.io/client-go/pkg/apis/clientauthentication/install"
+	clientauthenticationv1 "k8s.io/client-go/pkg/apis/clientauthentication/v1"
+	clientauthenticationv1beta1 "k8s.io/client-go/pkg/apis/clientauthentication/v1beta1"
+	"k8s.io/client-go/tools/clientcmd/api"
+	"k8s.io/client-go/tools/metrics"
+	"k8s.io/client-go/transport"
+	"k8s.io/client-go/util/connrotation"
+	"k8s.io/klog/v2"
+	"k8s.io/utils/clock"
+)
+
+const execInfoEnv = "KUBERNETES_EXEC_INFO"
+const installHintVerboseHelp = `
+
+It looks like you are trying to use a client-go credential plugin that is not installed.
+
+To learn more about this feature, consult the documentation available at:
+      https://kubernetes.io/docs/reference/access-authn-authz/authentication/#client-go-credential-plugins`
+
+var scheme = runtime.NewScheme()
+var codecs = serializer.NewCodecFactory(scheme)
+
+func init() {
+	install.Install(scheme)
+}
+
+var (
+	// Since transports can be constantly re-initialized by programs like kubectl,
+	// keep a cache of initialized authenticators keyed by a hash of their config.
+	globalCache = newCache()
+	// The list of API versions we accept.
+	apiVersions = map[string]schema.GroupVersion{
+		clientauthenticationv1beta1.SchemeGroupVersion.String(): clientauthenticationv1beta1.SchemeGroupVersion,
+		clientauthenticationv1.SchemeGroupVersion.String():      clientauthenticationv1.SchemeGroupVersion,
+	}
+)
+
+func newCache() *cache {
+	return &cache{m: make(map[string]*Authenticator)}
+}
+
+func cacheKey(conf *api.ExecConfig, cluster *clientauthentication.Cluster) string {
+	key := struct {
+		conf    *api.ExecConfig
+		cluster *clientauthentication.Cluster
+	}{
+		conf:    conf,
+		cluster: cluster,
+	}
+	return dump.Pretty(key)
+}
+
+type cache struct {
+	mu sync.Mutex
+	m  map[string]*Authenticator
+}
+
+func (c *cache) get(s string) (*Authenticator, bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	a, ok := c.m[s]
+	return a, ok
+}
+
+// put inserts an authenticator into the cache. If an authenticator is already
+// associated with the key, the first one is returned instead.
+func (c *cache) put(s string, a *Authenticator) *Authenticator {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	existing, ok := c.m[s]
+	if ok {
+		return existing
+	}
+	c.m[s] = a
+	return a
+}
+
+// sometimes rate limits how often a function f() is called. Specifically, Do()
+// will run the provided function f() up to threshold times every interval
+// duration.
+type sometimes struct {
+	threshold int
+	interval  time.Duration
+
+	clock clock.Clock
+	mu    sync.Mutex
+
+	count  int       // times we have called f() in this window
+	window time.Time // beginning of current window of length interval
+}
+
+func (s *sometimes) Do(f func()) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	now := s.clock.Now()
+	if s.window.IsZero() {
+		s.window = now
+	}
+
+	// If we are no longer in our saved time window, then we get to reset our run
+	// count back to 0 and start increasing towards the threshold again.
+	if inWindow := now.Sub(s.window) < s.interval; !inWindow {
+		s.window = now
+		s.count = 0
+	}
+
+	// If we have not run the function more than threshold times in this current
+	// time window, we get to run it now!
+	if underThreshold := s.count < s.threshold; underThreshold {
+		s.count++
+		f()
+	}
+}
+
+// GetAuthenticator returns an exec-based plugin for providing client credentials.
+func GetAuthenticator(config *api.ExecConfig, cluster *clientauthentication.Cluster) (*Authenticator, error) {
+	return newAuthenticator(globalCache, term.IsTerminal, config, cluster)
+}
+
+func newAuthenticator(c *cache, isTerminalFunc func(int) bool, config *api.ExecConfig, cluster *clientauthentication.Cluster) (*Authenticator, error) {
+	key := cacheKey(config, cluster)
+	if a, ok := c.get(key); ok {
+		return a, nil
+	}
+
+	gv, ok := apiVersions[config.APIVersion]
+	if !ok {
+		return nil, fmt.Errorf("exec plugin: invalid apiVersion %q", config.APIVersion)
+	}
+
+	connTracker := connrotation.NewConnectionTracker()
+	defaultDialer := connrotation.NewDialerWithTracker(
+		(&net.Dialer{Timeout: 30 * time.Second, KeepAlive: 30 * time.Second}).DialContext,
+		connTracker,
+	)
+
+	if err := ValidatePluginPolicy(config.PluginPolicy); err != nil {
+		return nil, fmt.Errorf("invalid plugin policy: %w", err)
+	}
+
+	allowlistLookup := sets.New[string]()
+	for _, entry := range config.PluginPolicy.Allowlist {
+		if entry.Name != "" {
+			allowlistLookup.Insert(entry.Name)
+		}
+	}
+
+	a := &Authenticator{
+		// Clean is called to normalize the path to facilitate comparison with
+		// the allowlist, when present
+		cmd:                filepath.Clean(config.Command),
+		args:               config.Args,
+		group:              gv,
+		cluster:            cluster,
+		provideClusterInfo: config.ProvideClusterInfo,
+
+		allowlistLookup:  allowlistLookup,
+		execPluginPolicy: config.PluginPolicy,
+
+		installHint: config.InstallHint,
+		sometimes: &sometimes{
+			threshold: 10,
+			interval:  time.Hour,
+			clock:     clock.RealClock{},
+		},
+
+		stdin:           os.Stdin,
+		stderr:          os.Stderr,
+		interactiveFunc: func() (bool, error) { return isInteractive(isTerminalFunc, config) },
+		now:             time.Now,
+		environ:         os.Environ,
+
+		connTracker: connTracker,
+	}
+
+	for _, env := range config.Env {
+		a.env = append(a.env, env.Name+"="+env.Value)
+	}
+
+	// these functions are made comparable and stored in the cache so that repeated clientset
+	// construction with the same rest.Config results in a single TLS cache and Authenticator
+	a.getCert = &transport.GetCertHolder{GetCert: a.cert}
+	a.dial = &transport.DialHolder{Dial: defaultDialer.DialContext}
+
+	return c.put(key, a), nil
+}
+
+func isInteractive(isTerminalFunc func(int) bool, config *api.ExecConfig) (bool, error) {
+	var shouldBeInteractive bool
+	switch config.InteractiveMode {
+	case api.NeverExecInteractiveMode:
+		shouldBeInteractive = false
+	case api.IfAvailableExecInteractiveMode:
+		shouldBeInteractive = !config.StdinUnavailable && isTerminalFunc(int(os.Stdin.Fd()))
+	case api.AlwaysExecInteractiveMode:
+		if !isTerminalFunc(int(os.Stdin.Fd())) {
+			return false, errors.New("standard input is not a terminal")
+		}
+		if config.StdinUnavailable {
+			suffix := ""
+			if len(config.StdinUnavailableMessage) > 0 {
+				// only print extra ": <message>" if the user actually specified a message
+				suffix = fmt.Sprintf(": %s", config.StdinUnavailableMessage)
+			}
+			return false, fmt.Errorf("standard input is unavailable%s", suffix)
+		}
+		shouldBeInteractive = true
+	default:
+		return false, fmt.Errorf("unknown interactiveMode: %q", config.InteractiveMode)
+	}
+
+	return shouldBeInteractive, nil
+}
+
+// Authenticator is a client credential provider that rotates credentials by executing a plugin.
+// The plugin input and output are defined by the API group client.authentication.k8s.io.
+type Authenticator struct {
+	// Set by the config
+	cmd                string
+	args               []string
+	group              schema.GroupVersion
+	env                []string
+	cluster            *clientauthentication.Cluster
+	provideClusterInfo bool
+
+	allowlistLookup  sets.Set[string]
+	execPluginPolicy api.PluginPolicy
+
+	// Used to avoid log spew by rate limiting install hint printing. We didn't do
+	// this by interval based rate limiting alone since that way may have prevented
+	// the install hint from showing up for kubectl users.
+	sometimes   *sometimes
+	installHint string
+
+	// Stubbable for testing
+	stdin           io.Reader
+	stderr          io.Writer
+	interactiveFunc func() (bool, error)
+	now             func() time.Time
+	environ         func() []string
+
+	// connTracker tracks all connections opened that we need to close when rotating a client certificate
+	connTracker *connrotation.ConnectionTracker
+
+	// Cached results.
+	//
+	// The mutex also guards calling the plugin. Since the plugin could be
+	// interactive we want to make sure it's only called once.
+	mu          sync.Mutex
+	cachedCreds *credentials
+	exp         time.Time
+
+	// getCert makes Authenticator.cert comparable to support TLS config caching
+	getCert *transport.GetCertHolder
+	// dial is used for clients which do not specify a custom dialer
+	// it is comparable to support TLS config caching
+	dial *transport.DialHolder
+}
+
+type credentials struct {
+	token string           `datapolicy:"token"`
+	cert  *tls.Certificate `datapolicy:"secret-key"`
+}
+
+// UpdateTransportConfig updates the transport.Config to use credentials
+// returned by the plugin.
+func (a *Authenticator) UpdateTransportConfig(c *transport.Config) error {
+	// If a bearer token is present in the request - avoid the GetCert callback when
+	// setting up the transport, as that triggers the exec action if the server is
+	// also configured to allow client certificates for authentication. For requests
+	// like "kubectl get --token (token) pods" we should assume the intention is to
+	// use the provided token for authentication. The same can be said for when the
+	// user specifies basic auth or cert auth.
+	if c.HasTokenAuth() || c.HasBasicAuth() || c.HasCertAuth() {
+		return nil
+	}
+
+	c.Wrap(func(rt http.RoundTripper) http.RoundTripper {
+		return &roundTripper{a, rt}
+	})
+
+	if c.HasCertCallback() {
+		return errors.New("can't add TLS certificate callback: transport.Config.TLS.GetCert already set")
+	}
+	c.TLS.GetCertHolder = a.getCert // comparable for TLS config caching
+
+	if c.DialHolder != nil {
+		if c.DialHolder.Dial == nil {
+			return errors.New("invalid transport.Config.DialHolder: wrapped Dial function is nil")
+		}
+
+		// if c has a custom dialer, we have to wrap it
+		// TLS config caching is not supported for this config
+		d := connrotation.NewDialerWithTracker(c.DialHolder.Dial, a.connTracker)
+		c.DialHolder = &transport.DialHolder{Dial: d.DialContext}
+	} else {
+		c.DialHolder = a.dial // comparable for TLS config caching
+	}
+
+	return nil
+}
+
+var _ utilnet.RoundTripperWrapper = &roundTripper{}
+
+type roundTripper struct {
+	a    *Authenticator
+	base http.RoundTripper
+}
+
+func (r *roundTripper) WrappedRoundTripper() http.RoundTripper {
+	return r.base
+}
+
+func (r *roundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	// If a user has already set credentials, use that. This makes commands like
+	// "kubectl get --token (token) pods" work.
+	if req.Header.Get("Authorization") != "" {
+		return r.base.RoundTrip(req)
+	}
+
+	creds, err := r.a.getCreds()
+	if err != nil {
+		return nil, fmt.Errorf("getting credentials: %v", err)
+	}
+	if creds.token != "" {
+		req.Header.Set("Authorization", "Bearer "+creds.token)
+	}
+
+	res, err := r.base.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+	if res.StatusCode == http.StatusUnauthorized {
+		if err := r.a.maybeRefreshCreds(creds); err != nil {
+			klog.Errorf("refreshing credentials: %v", err)
+		}
+	}
+	return res, nil
+}
+
+func (a *Authenticator) credsExpired() bool {
+	if a.exp.IsZero() {
+		return false
+	}
+	return a.now().After(a.exp)
+}
+
+func (a *Authenticator) cert() (*tls.Certificate, error) {
+	creds, err := a.getCreds()
+	if err != nil {
+		return nil, err
+	}
+	return creds.cert, nil
+}
+
+func (a *Authenticator) getCreds() (*credentials, error) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	if a.cachedCreds != nil && !a.credsExpired() {
+		return a.cachedCreds, nil
+	}
+
+	if err := a.refreshCredsLocked(); err != nil {
+		return nil, err
+	}
+
+	return a.cachedCreds, nil
+}
+
+// maybeRefreshCreds executes the plugin to force a rotation of the
+// credentials, unless they were rotated already.
+func (a *Authenticator) maybeRefreshCreds(creds *credentials) error {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+
+	// Since we're not making a new pointer to a.cachedCreds in getCreds, no
+	// need to do deep comparison.
+	if creds != a.cachedCreds {
+		// Credentials already rotated.
+		return nil
+	}
+
+	return a.refreshCredsLocked()
+}
+
+// refreshCredsLocked executes the plugin and reads the credentials from
+// stdout. It must be called while holding the Authenticator's mutex.
+func (a *Authenticator) refreshCredsLocked() error {
+	interactive, err := a.interactiveFunc()
+	if err != nil {
+		return fmt.Errorf("exec plugin cannot support interactive mode: %w", err)
+	}
+
+	cred := &clientauthentication.ExecCredential{
+		Spec: clientauthentication.ExecCredentialSpec{
+			Interactive: interactive,
+		},
+	}
+	if a.provideClusterInfo {
+		cred.Spec.Cluster = a.cluster
+	}
+
+	env := append(a.environ(), a.env...)
+	data, err := runtime.Encode(codecs.LegacyCodec(a.group), cred)
+	if err != nil {
+		return fmt.Errorf("encode ExecCredentials: %v", err)
+	}
+	env = append(env, fmt.Sprintf("%s=%s", execInfoEnv, data))
+
+	stdout := &bytes.Buffer{}
+	cmd := exec.Command(a.cmd, a.args...)
+	cmd.Env = env
+	cmd.Stderr = a.stderr
+	cmd.Stdout = stdout
+	if interactive {
+		cmd.Stdin = a.stdin
+	}
+
+	err = a.updateCommandAndCheckAllowlistLocked(cmd)
+	incrementPolicyMetric(err)
+	if err != nil {
+		return err
+	}
+
+	err = cmd.Run()
+	incrementCallsMetric(err)
+	if err != nil {
+		return a.wrapCmdRunErrorLocked(err)
+	}
+
+	_, gvk, err := codecs.UniversalDecoder(a.group).Decode(stdout.Bytes(), nil, cred)
+	if err != nil {
+		return fmt.Errorf("decoding stdout: %v", err)
+	}
+	if gvk.Group != a.group.Group || gvk.Version != a.group.Version {
+		return fmt.Errorf("exec plugin is configured to use API version %s, plugin returned version %s",
+			a.group, schema.GroupVersion{Group: gvk.Group, Version: gvk.Version})
+	}
+
+	if cred.Status == nil {
+		return fmt.Errorf("exec plugin didn't return a status field")
+	}
+	if cred.Status.Token == "" && cred.Status.ClientCertificateData == "" && cred.Status.ClientKeyData == "" {
+		return fmt.Errorf("exec plugin didn't return a token or cert/key pair")
+	}
+	if (cred.Status.ClientCertificateData == "") != (cred.Status.ClientKeyData == "") {
+		return fmt.Errorf("exec plugin returned only certificate or key, not both")
+	}
+
+	if cred.Status.ExpirationTimestamp != nil {
+		a.exp = cred.Status.ExpirationTimestamp.Time
+	} else {
+		a.exp = time.Time{}
+	}
+
+	newCreds := &credentials{
+		token: cred.Status.Token,
+	}
+	if cred.Status.ClientKeyData != "" && cred.Status.ClientCertificateData != "" {
+		cert, err := tls.X509KeyPair([]byte(cred.Status.ClientCertificateData), []byte(cred.Status.ClientKeyData))
+		if err != nil {
+			return fmt.Errorf("failed parsing client key/certificate: %v", err)
+		}
+
+		// Leaf is initialized to be nil:
+		//  https://golang.org/pkg/crypto/tls/#X509KeyPair
+		// Leaf certificate is the first certificate:
+		//  https://golang.org/pkg/crypto/tls/#Certificate
+		// Populating leaf is useful for quickly accessing the underlying x509
+		// certificate values.
+		cert.Leaf, err = x509.ParseCertificate(cert.Certificate[0])
+		if err != nil {
+			return fmt.Errorf("failed parsing client leaf certificate: %v", err)
+		}
+		newCreds.cert = &cert
+	}
+
+	oldCreds := a.cachedCreds
+	a.cachedCreds = newCreds
+	// Only close all connections when TLS cert rotates. Token rotation doesn't
+	// need the extra noise.
+	if oldCreds != nil && !reflect.DeepEqual(oldCreds.cert, a.cachedCreds.cert) {
+		// Can be nil if the exec auth plugin only returned token auth.
+		if oldCreds.cert != nil && oldCreds.cert.Leaf != nil {
+			metrics.ClientCertRotationAge.Observe(time.Since(oldCreds.cert.Leaf.NotBefore))
+		}
+		a.connTracker.CloseAll()
+	}
+
+	expiry := time.Time{}
+	if a.cachedCreds.cert != nil && a.cachedCreds.cert.Leaf != nil {
+		expiry = a.cachedCreds.cert.Leaf.NotAfter
+	}
+	expirationMetrics.set(a, expiry)
+	return nil
+}
+
+// wrapCmdRunErrorLocked pulls out the code to construct a helpful error message
+// for when the exec plugin's binary fails to Run().
+//
+// It must be called while holding the Authenticator's mutex.
+func (a *Authenticator) wrapCmdRunErrorLocked(err error) error {
+	switch err.(type) {
+	case *exec.Error: // Binary does not exist (see exec.Error).
+		builder := strings.Builder{}
+		fmt.Fprintf(&builder, "exec: executable %s not found", a.cmd)
+
+		a.sometimes.Do(func() {
+			fmt.Fprint(&builder, installHintVerboseHelp)
+			if a.installHint != "" {
+				fmt.Fprintf(&builder, "\n\n%s", a.installHint)
+			}
+		})
+
+		return errors.New(builder.String())
+
+	case *exec.ExitError: // Binary execution failed (see exec.Cmd.Run()).
+		e := err.(*exec.ExitError)
+		return fmt.Errorf(
+			"exec: executable %s failed with exit code %d",
+			a.cmd,
+			e.ProcessState.ExitCode(),
+		)
+
+	default:
+		return fmt.Errorf("exec: %v", err)
+	}
+}
+
+// `updateCommandAndCheckAllowlistLocked` determines whether or not the specified executable may run
+// according to the credential plugin policy. If the plugin is allowed, `nil`
+// is returned. If the plugin is not allowed, an error must be returned
+// explaining why.
+func (a *Authenticator) updateCommandAndCheckAllowlistLocked(cmd *exec.Cmd) error {
+	switch a.execPluginPolicy.PolicyType {
+	case "", api.PluginPolicyAllowAll:
+		return nil
+	case api.PluginPolicyDenyAll:
+		return fmt.Errorf("plugin %q not allowed: policy set to %q", a.cmd, api.PluginPolicyDenyAll)
+	case api.PluginPolicyAllowlist:
+		return a.checkAllowlistLocked(cmd)
+	default:
+		return fmt.Errorf("unknown plugin policy %q", a.execPluginPolicy.PolicyType)
+	}
+}
+
+// `checkAllowlistLocked` checks the specified plugin against the allowlist,
+// and may update the Authenticator's allowlistLookup set.
+func (a *Authenticator) checkAllowlistLocked(cmd *exec.Cmd) error {
+	// a.cmd is the original command as specified in the configuration, then filepath.Clean().
+	// cmd.Path is the possibly-resolved command.
+	// If either are an exact match in the allowlist, return success.
+	if a.allowlistLookup.Has(a.cmd) || a.allowlistLookup.Has(cmd.Path) {
+		return nil
+	}
+
+	var cmdResolvedPath string
+	var cmdResolvedErr error
+	if cmd.Path != a.cmd {
+		// cmd.Path changed, use the already-resolved LookPath results
+		cmdResolvedPath = cmd.Path
+		cmdResolvedErr = cmd.Err
+	} else {
+		// cmd.Path is unchanged, do LookPath ourselves
+		cmdResolvedPath, cmdResolvedErr = exec.LookPath(cmd.Path)
+		// update cmd.Path to cmdResolvedPath so we only run the resolved path
+		if cmdResolvedPath != "" {
+			cmd.Path = cmdResolvedPath
+		}
+	}
+
+	if cmdResolvedErr != nil {
+		return fmt.Errorf("plugin path %q cannot be resolved for credential plugin allowlist check: %w", cmd.Path, cmdResolvedErr)
+	}
+
+	// cmdResolvedPath may have changed, and the changed value may be in the allowlist
+	if a.allowlistLookup.Has(cmdResolvedPath) {
+		return nil
+	}
+
+	// There is no verbatim match
+	a.resolveAllowListEntriesLocked(cmd.Path)
+
+	// allowlistLookup may have changed, recheck
+	if a.allowlistLookup.Has(cmdResolvedPath) {
+		return nil
+	}
+
+	return fmt.Errorf("plugin path %q is not permitted by the credential plugin allowlist", cmd.Path)
+}
+
+// resolveAllowListEntriesLocked tries to resolve allowlist entries with LookPath,
+// and adds successfully resolved entries to allowlistLookup.
+// The optional commandHint can be used to limit which entries are resolved to ones which match the hint basename.
+func (a *Authenticator) resolveAllowListEntriesLocked(commandHint string) {
+	hintName := filepath.Base(commandHint)
+	for _, entry := range a.execPluginPolicy.Allowlist {
+		entryBasename := filepath.Base(entry.Name)
+		if hintName != "" && hintName != entryBasename {
+			// we got a hint, and this allowlist entry does not match it
+			continue
+		}
+		entryResolvedPath, err := exec.LookPath(entry.Name)
+		if err != nil {
+			klog.V(5).ErrorS(err, "resolving credential plugin allowlist", "name", entry.Name)
+			continue
+		}
+		if entryResolvedPath != "" {
+			a.allowlistLookup.Insert(entryResolvedPath)
+		}
+	}
+}
+
+func ValidatePluginPolicy(policy api.PluginPolicy) error {
+	switch policy.PolicyType {
+	// "" is equivalent to "AllowAll"
+	case "", api.PluginPolicyAllowAll, api.PluginPolicyDenyAll:
+		if policy.Allowlist != nil {
+			return fmt.Errorf("misconfigured credential plugin allowlist: plugin policy is %q but allowlist is non-nil", policy.PolicyType)
+		}
+		return nil
+	case api.PluginPolicyAllowlist:
+		return validateAllowlist(policy.Allowlist)
+	default:
+		return fmt.Errorf("unknown plugin policy: %q", policy.PolicyType)
+	}
+}
+
+var emptyAllowlistEntry api.AllowlistEntry
+
+func validateAllowlist(list []api.AllowlistEntry) error {
+	// This will be the case if the user has misspelled the field name for the
+	// allowlist. Because this is a security knob, fail immediately rather than
+	// proceed when the user has made a mistake.
+	if list == nil {
+		return fmt.Errorf("credential plugin policy set to %q, but allowlist is unspecified", api.PluginPolicyAllowlist)
+	}
+
+	if len(list) == 0 {
+		return fmt.Errorf("credential plugin policy set to %q, but allowlist is empty; use %q policy instead", api.PluginPolicyAllowlist, api.PluginPolicyDenyAll)
+	}
+
+	for i, item := range list {
+		if item == emptyAllowlistEntry {
+			return fmt.Errorf("misconfigured credential plugin allowlist: empty allowlist entry #%d", i+1)
+		}
+
+		if cleaned := filepath.Clean(item.Name); cleaned != item.Name {
+			return fmt.Errorf("non-normalized file path: %q vs %q", item.Name, cleaned)
+		} else if item.Name == "" {
+			return fmt.Errorf("empty file path: %q", item.Name)
+		}
+	}
+
+	return nil
+}

vendor/k8s.io/client-go/plugin/pkg/client/auth/exec/metrics.go

@@ -0,0 +1,127 @@
+/*
+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.
+*/
+
+package exec
+
+import (
+	"errors"
+	"io/fs"
+	"os/exec"
+	"reflect"
+	"sync"
+	"time"
+
+	"k8s.io/klog/v2"
+
+	"k8s.io/client-go/tools/metrics"
+)
+
+// The following constants shadow the special values used in the prometheus metrics implementation.
+const (
+	// noError indicates that the plugin process was successfully started and exited with an exit
+	// code of 0.
+	noError = "no_error"
+	// pluginExecutionError indicates that the plugin process was successfully started and then
+	// it returned a non-zero exit code.
+	pluginExecutionError = "plugin_execution_error"
+	// pluginNotFoundError indicates that we could not find the exec plugin.
+	pluginNotFoundError = "plugin_not_found_error"
+	// clientInternalError indicates that we attempted to start the plugin process, but failed
+	// for some reason.
+	clientInternalError = "client_internal_error"
+
+	// successExitCode represents an exec plugin invocation that was successful.
+	successExitCode = 0
+	// failureExitCode represents an exec plugin invocation that was not successful. This code is
+	// used in some failure modes (e.g., plugin not found, client internal error) so that someone
+	// can more easily monitor all unsuccessful invocations.
+	failureExitCode = 1
+
+	// pluginAllowed represents an exec plugin invocation that was allowed by
+	// the plugin policy and/or the allowlist
+	pluginAllowed = "allowed"
+	// pluginAllowed represents an exec plugin invocation that was denied by
+	// the plugin policy and/or the allowlist
+	pluginDenied = "denied"
+)
+
+type certificateExpirationTracker struct {
+	mu        sync.RWMutex
+	m         map[*Authenticator]time.Time
+	metricSet func(*time.Time)
+}
+
+var expirationMetrics = &certificateExpirationTracker{
+	m: map[*Authenticator]time.Time{},
+	metricSet: func(e *time.Time) {
+		metrics.ClientCertExpiry.Set(e)
+	},
+}
+
+// set stores the given expiration time and updates the updates the certificate
+// expiry metric to the earliest expiration time.
+func (c *certificateExpirationTracker) set(a *Authenticator, t time.Time) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.m[a] = t
+
+	earliest := time.Time{}
+	for _, t := range c.m {
+		if t.IsZero() {
+			continue
+		}
+		if earliest.IsZero() || earliest.After(t) {
+			earliest = t
+		}
+	}
+	if earliest.IsZero() {
+		c.metricSet(nil)
+	} else {
+		c.metricSet(&earliest)
+	}
+}
+
+// incrementCallsMetric increments a global metrics counter for the number of calls to an exec
+// plugin, partitioned by exit code. The provided err should be the return value from
+// exec.Cmd.Run().
+func incrementCallsMetric(err error) {
+	execExitError := &exec.ExitError{}
+	execError := &exec.Error{}
+	pathError := &fs.PathError{}
+	switch {
+	case err == nil: // Binary execution succeeded.
+		metrics.ExecPluginCalls.Increment(successExitCode, noError)
+
+	case errors.As(err, &execExitError): // Binary execution failed (see "os/exec".Cmd.Run()).
+		metrics.ExecPluginCalls.Increment(execExitError.ExitCode(), pluginExecutionError)
+
+	case errors.As(err, &execError), errors.As(err, &pathError): // Binary does not exist (see exec.Error, fs.PathError).
+		metrics.ExecPluginCalls.Increment(failureExitCode, pluginNotFoundError)
+
+	default: // We don't know about this error type.
+		klog.V(2).InfoS("unexpected exec plugin return error type", "type", reflect.TypeOf(err).String(), "err", err)
+		metrics.ExecPluginCalls.Increment(failureExitCode, clientInternalError)
+	}
+}
+
+func incrementPolicyMetric(err error) {
+	if err != nil {
+		metrics.ExecPluginPolicyCalls.Increment(pluginDenied)
+		return
+	}
+
+	metrics.ExecPluginPolicyCalls.Increment(pluginAllowed)
+}