Merge pull request #123282 from enj/enj/i/authn_config_algs

Support all key algs with structured authn config

pkg/kubeapiserver/options/authentication.go

@@ -40,6 +40,7 @@ import (
 	"k8s.io/apiserver/pkg/server/egressselector"
 	genericoptions "k8s.io/apiserver/pkg/server/options"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/apiserver/plugin/pkg/authenticator/token/oidc"
 	"k8s.io/client-go/informers"
 	"k8s.io/client-go/kubernetes"
 	v1listers "k8s.io/client-go/listers/core/v1"
@@ -461,6 +462,9 @@ func (o *BuiltInAuthenticationOptions) ToAuthenticationConfig() (kubeauthenticat
 		if ret.AuthenticationConfig, err = loadAuthenticationConfig(o.AuthenticationConfigFile); err != nil {
 			return kubeauthenticator.Config{}, err
 		}
+		// all known signing algs are allowed when using authentication config
+		// TODO: what we really want to express is 'any alg is fine as long it matches a public key'
+		ret.OIDCSigningAlgs = oidc.AllValidSigningAlgorithms()
 	} else if o.OIDC != nil && len(o.OIDC.IssuerURL) > 0 && len(o.OIDC.ClientID) > 0 {
 		usernamePrefix := o.OIDC.UsernamePrefix
 

pkg/kubeapiserver/options/authentication_test.go

@@ -446,6 +446,8 @@ func TestBuiltInAuthenticationOptionsAddFlags(t *testing.T) {
 }
 
 func TestToAuthenticationConfig_OIDC(t *testing.T) {
+	defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.StructuredAuthenticationConfiguration, true)()
+
 	testCases := []struct {
 		name         string
 		args         []string
@@ -640,6 +642,43 @@ func TestToAuthenticationConfig_OIDC(t *testing.T) {
 				OIDCSigningAlgs: []string{"RS256"},
 			},
 		},
+		{
+			name: "basic authentication configuration",
+			args: []string{
+				"--authentication-config=" + writeTempFile(t, `
+apiVersion: apiserver.config.k8s.io/v1alpha1
+kind: AuthenticationConfiguration
+jwt:
+- issuer:
+    url: https://test-issuer
+    audiences: [ "🐼" ]
+  claimMappings:
+    username:
+      claim: sub
+      prefix: ""
+`),
+			},
+			expectConfig: kubeauthenticator.Config{
+				TokenSuccessCacheTTL: 10 * time.Second,
+				AuthenticationConfig: &apiserver.AuthenticationConfiguration{
+					JWT: []apiserver.JWTAuthenticator{
+						{
+							Issuer: apiserver.Issuer{
+								URL:       "https://test-issuer",
+								Audiences: []string{"🐼"},
+							},
+							ClaimMappings: apiserver.ClaimMappings{
+								Username: apiserver.PrefixedClaimOrExpression{
+									Claim:  "sub",
+									Prefix: pointer.String(""),
+								},
+							},
+						},
+					},
+				},
+				OIDCSigningAlgs: []string{"ES256", "ES384", "ES512", "PS256", "PS384", "PS512", "RS256", "RS384", "RS512"},
+			},
+		},
 	}
 
 	for _, testcase := range testCases {

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

@@ -204,8 +204,11 @@ func (a *Authenticator) Close() {
 	a.cancel()
 }
 
-// whitelist of signing algorithms to ensure users don't mistakenly pass something
-// goofy.
+func AllValidSigningAlgorithms() []string {
+	return sets.List(sets.KeySet(allowedSigningAlgs))
+}
+
+// allowlist of signing algorithms to ensure users don't mistakenly pass something goofy.
 var allowedSigningAlgs = map[string]bool{
 	oidc.RS256: true,
 	oidc.RS384: true,

test/integration/apiserver/oidc/oidc_test.go

@@ -18,6 +18,8 @@ package oidc
 
 import (
 	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/tls"
@@ -35,11 +37,13 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"gopkg.in/square/go-jose.v2"
 
 	authenticationv1 "k8s.io/api/authentication/v1"
 	rbacv1 "k8s.io/api/rbac/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	utilrand "k8s.io/apimachinery/pkg/util/rand"
 	"k8s.io/apiserver/pkg/features"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	"k8s.io/client-go/kubernetes"
@@ -116,29 +120,10 @@ func TestStructuredAuthenticationConfig(t *testing.T) {
 }
 
 func runTests(t *testing.T, useAuthenticationConfig bool) {
-	var tests = []struct {
-		name                    string
-		configureInfrastructure func(t *testing.T, fn authenticationConfigFunc) (
-			oidcServer *utilsoidc.TestServer,
-			apiServer *kubeapiserverapptesting.TestServer,
-			signingPrivateKey *rsa.PrivateKey,
-			caCertContent []byte,
-			caFilePath string,
-		)
-		configureOIDCServerBehaviour func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey)
-		configureClient              func(
-			t *testing.T,
-			restCfg *rest.Config,
-			caCert []byte,
-			certPath,
-			oidcServerURL,
-			oidcServerTokenURL string,
-		) kubernetes.Interface
-		assertErrFn func(t *testing.T, errorToCheck error)
-	}{
+	var tests = []singleTest[*rsa.PrivateKey, *rsa.PublicKey]{
 		{
 			name:                    "ID token is ok",
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -161,7 +146,7 @@ func runTests(t *testing.T, useAuthenticationConfig bool) {
 		},
 		{
 			name:                    "ID token is expired",
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				configureOIDCServerToReturnExpiredIDToken(t, 2, oidcServer, signingPrivateKey)
 			},
@@ -172,7 +157,7 @@ func runTests(t *testing.T, useAuthenticationConfig bool) {
 		},
 		{
 			name:                    "wrong client ID",
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, _ *rsa.PrivateKey) {
 				oidcServer.TokenHandler().EXPECT().Token().Times(2).Return(utilsoidc.Token{}, utilsoidc.ErrBadClientID)
 			},
@@ -189,7 +174,7 @@ func runTests(t *testing.T, useAuthenticationConfig bool) {
 		},
 		{
 			name:                         "client has wrong CA",
-			configureInfrastructure:      configureTestInfrastructure,
+			configureInfrastructure:      configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, _ *rsa.PrivateKey) {},
 			configureClient: func(t *testing.T, restCfg *rest.Config, caCert []byte, _, oidcServerURL, oidcServerTokenURL string) kubernetes.Interface {
 				tempDir := t.TempDir()
@@ -207,7 +192,7 @@ func runTests(t *testing.T, useAuthenticationConfig bool) {
 		},
 		{
 			name:                    "refresh flow does not return ID Token",
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				configureOIDCServerToReturnExpiredIDToken(t, 1, oidcServer, signingPrivateKey)
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).Return(utilsoidc.Token{
@@ -230,7 +215,7 @@ func runTests(t *testing.T, useAuthenticationConfig bool) {
 		},
 		{
 			name: "ID token signature can not be verified due to wrong JWKs",
-			configureInfrastructure: func(t *testing.T, fn authenticationConfigFunc) (
+			configureInfrastructure: func(t *testing.T, fn authenticationConfigFunc, keyFunc func(t *testing.T) (*rsa.PrivateKey, *rsa.PublicKey)) (
 				oidcServer *utilsoidc.TestServer,
 				apiServer *kubeapiserverapptesting.TestServer,
 				signingPrivateKey *rsa.PrivateKey,
@@ -239,8 +224,7 @@ func runTests(t *testing.T, useAuthenticationConfig bool) {
 			) {
 				caCertContent, _, caFilePath, caKeyFilePath := generateCert(t)
 
-				signingPrivateKey, wantErr := rsa.GenerateKey(rand.Reader, rsaKeyBitSize)
-				require.NoError(t, wantErr)
+				signingPrivateKey, _ = keyFunc(t)
 
 				oidcServer = utilsoidc.BuildAndRunTestServer(t, caFilePath, caKeyFilePath)
 
@@ -260,16 +244,16 @@ jwt:
       claim: sub
       prefix: %s
 `, oidcServer.URL(), defaultOIDCClientID, indentCertificateAuthority(string(caCertContent)), defaultOIDCUsernamePrefix)
-					apiServer = startTestAPIServerForOIDC(t, "", "", "", authenticationConfig)
+					apiServer = startTestAPIServerForOIDC(t, "", "", "", authenticationConfig, &signingPrivateKey.PublicKey)
 				} else {
-					apiServer = startTestAPIServerForOIDC(t, oidcServer.URL(), defaultOIDCClientID, caFilePath, "")
+					apiServer = startTestAPIServerForOIDC(t, oidcServer.URL(), defaultOIDCClientID, caFilePath, "", &signingPrivateKey.PublicKey)
 				}
 
 				adminClient := kubernetes.NewForConfigOrDie(apiServer.ClientConfig)
 				configureRBAC(t, adminClient, defaultRole, defaultRoleBinding)
 
-				anotherSigningPrivateKey, wantErr := rsa.GenerateKey(rand.Reader, rsaKeyBitSize)
-				require.NoError(t, wantErr)
+				anotherSigningPrivateKey, _ := keyFunc(t)
+
 				oidcServer.JwksHandler().EXPECT().KeySet().AnyTimes().DoAndReturn(utilsoidc.DefaultJwksHandlerBehavior(t, &anotherSigningPrivateKey.PublicKey))
 
 				return oidcServer, apiServer, signingPrivateKey, caCertContent, caFilePath
@@ -296,11 +280,69 @@ jwt:
 	}
 
 	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			fn := func(t *testing.T, issuerURL, caCert string) string { return "" }
-			if useAuthenticationConfig {
-				fn = func(t *testing.T, issuerURL, caCert string) string {
-					return fmt.Sprintf(`
+		t.Run(tt.name, singleTestRunner(useAuthenticationConfig, rsaGenerateKey, tt))
+	}
+
+	for _, tt := range []singleTest[*ecdsa.PrivateKey, *ecdsa.PublicKey]{
+		{
+			name:                    "ID token is ok",
+			configureInfrastructure: configureTestInfrastructure[*ecdsa.PrivateKey, *ecdsa.PublicKey],
+			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *ecdsa.PrivateKey) {
+				idTokenLifetime := time.Second * 1200
+				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
+					t,
+					signingPrivateKey,
+					map[string]interface{}{
+						"iss": oidcServer.URL(),
+						"sub": defaultOIDCClaimedUsername,
+						"aud": defaultOIDCClientID,
+						"exp": time.Now().Add(idTokenLifetime).Unix(),
+					},
+					defaultStubAccessToken,
+					defaultStubRefreshToken,
+				))
+			},
+			configureClient: configureClientFetchingOIDCCredentials,
+			assertErrFn: func(t *testing.T, errorToCheck error) {
+				assert.NoError(t, errorToCheck)
+			},
+		},
+	} {
+		t.Run(tt.name, singleTestRunner(useAuthenticationConfig, ecdsaGenerateKey, tt))
+	}
+}
+
+type singleTest[K utilsoidc.JosePrivateKey, L utilsoidc.JosePublicKey] struct {
+	name                    string
+	configureInfrastructure func(t *testing.T, fn authenticationConfigFunc, keyFunc func(t *testing.T) (K, L)) (
+		oidcServer *utilsoidc.TestServer,
+		apiServer *kubeapiserverapptesting.TestServer,
+		signingPrivateKey K,
+		caCertContent []byte,
+		caFilePath string,
+	)
+	configureOIDCServerBehaviour func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey K)
+	configureClient              func(
+		t *testing.T,
+		restCfg *rest.Config,
+		caCert []byte,
+		certPath,
+		oidcServerURL,
+		oidcServerTokenURL string,
+	) kubernetes.Interface
+	assertErrFn func(t *testing.T, errorToCheck error)
+}
+
+func singleTestRunner[K utilsoidc.JosePrivateKey, L utilsoidc.JosePublicKey](
+	useAuthenticationConfig bool,
+	keyFunc func(t *testing.T) (K, L),
+	tt singleTest[K, L],
+) func(t *testing.T) {
+	return func(t *testing.T) {
+		fn := func(t *testing.T, issuerURL, caCert string) string { return "" }
+		if useAuthenticationConfig {
+			fn = func(t *testing.T, issuerURL, caCert string) string {
+				return fmt.Sprintf(`
 apiVersion: apiserver.config.k8s.io/v1alpha1
 kind: AuthenticationConfiguration
 jwt:
@@ -315,31 +357,32 @@ jwt:
       claim: sub
       prefix: %s
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert), defaultOIDCUsernamePrefix)
-				}
 			}
-			oidcServer, apiServer, signingPrivateKey, caCert, certPath := tt.configureInfrastructure(t, fn)
+		}
+		oidcServer, apiServer, signingPrivateKey, caCert, certPath := tt.configureInfrastructure(t, fn, keyFunc)
 
-			tt.configureOIDCServerBehaviour(t, oidcServer, signingPrivateKey)
+		tt.configureOIDCServerBehaviour(t, oidcServer, signingPrivateKey)
 
-			tokenURL, err := oidcServer.TokenURL()
-			require.NoError(t, err)
+		tokenURL, err := oidcServer.TokenURL()
+		require.NoError(t, err)
 
-			client := tt.configureClient(t, apiServer.ClientConfig, caCert, certPath, oidcServer.URL(), tokenURL)
+		client := tt.configureClient(t, apiServer.ClientConfig, caCert, certPath, oidcServer.URL(), tokenURL)
 
-			ctx := testContext(t)
-			_, err = client.CoreV1().Pods(defaultNamespace).List(ctx, metav1.ListOptions{})
+		ctx := testContext(t)
+		_, err = client.CoreV1().Pods(defaultNamespace).List(ctx, metav1.ListOptions{})
 
-			tt.assertErrFn(t, err)
-		})
+		tt.assertErrFn(t, err)
 	}
 }
 
 func TestUpdatingRefreshTokenInCaseOfExpiredIDToken(t *testing.T) {
-	var tests = []struct {
+	type testRun[K utilsoidc.JosePrivateKey] struct {
 		name                            string
-		configureUpdatingTokenBehaviour func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey)
+		configureUpdatingTokenBehaviour func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey K)
 		assertErrFn                     func(t *testing.T, errorToCheck error)
-	}{
+	}
+
+	var tests = []testRun[*rsa.PrivateKey]{
 		{
 			name: "cache returns stale client if refresh token is not updated in config",
 			configureUpdatingTokenBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
@@ -369,7 +412,7 @@ func TestUpdatingRefreshTokenInCaseOfExpiredIDToken(t *testing.T) {
 		},
 	}
 
-	oidcServer, apiServer, signingPrivateKey, caCert, certPath := configureTestInfrastructure(t, func(t *testing.T, _, _ string) string { return "" })
+	oidcServer, apiServer, signingPrivateKey, caCert, certPath := configureTestInfrastructure(t, func(t *testing.T, _, _ string) string { return "" }, rsaGenerateKey)
 
 	tokenURL, err := oidcServer.TokenURL()
 	require.NoError(t, err)
@@ -399,17 +442,17 @@ func TestUpdatingRefreshTokenInCaseOfExpiredIDToken(t *testing.T) {
 func TestStructuredAuthenticationConfigCEL(t *testing.T) {
 	defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.StructuredAuthenticationConfiguration, true)()
 
-	tests := []struct {
+	type testRun[K utilsoidc.JosePrivateKey, L utilsoidc.JosePublicKey] struct {
 		name                    string
 		authConfigFn            authenticationConfigFunc
-		configureInfrastructure func(t *testing.T, fn authenticationConfigFunc) (
+		configureInfrastructure func(t *testing.T, fn authenticationConfigFunc, keyFunc func(t *testing.T) (K, L)) (
 			oidcServer *utilsoidc.TestServer,
 			apiServer *kubeapiserverapptesting.TestServer,
 			signingPrivateKey *rsa.PrivateKey,
 			caCertContent []byte,
 			caFilePath string,
 		)
-		configureOIDCServerBehaviour func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey)
+		configureOIDCServerBehaviour func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey K)
 		configureClient              func(
 			t *testing.T,
 			restCfg *rest.Config,
@@ -420,7 +463,9 @@ func TestStructuredAuthenticationConfigCEL(t *testing.T) {
 		) kubernetes.Interface
 		assertErrFn func(t *testing.T, errorToCheck error)
 		wantUser    *authenticationv1.UserInfo
-	}{
+	}
+
+	tests := []testRun[*rsa.PrivateKey, *rsa.PublicKey]{
 		{
 			name: "username CEL expression is ok",
 			authConfigFn: func(t *testing.T, issuerURL, caCert string) string {
@@ -441,7 +486,7 @@ jwt:
       expression: "'k8s-' + claims.sub"
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert))
 			},
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -488,7 +533,7 @@ jwt:
       expression: '(claims.roles.split(",") + claims.other_roles.split(",")).map(role, "prefix:" + role)'
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert))
 			},
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -538,7 +583,7 @@ jwt:
     message: "the hd claim must be set to example.com"
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert))
 			},
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -588,7 +633,7 @@ jwt:
     message: "example.org/foo must be bar and example.org/baz must be qux"
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert))
 			},
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -640,7 +685,7 @@ jwt:
       expression: "claims.uid"
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert))
 			},
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -692,7 +737,7 @@ jwt:
     message: "groups cannot used reserved system: prefix"
 `, issuerURL, defaultOIDCClientID, indentCertificateAuthority(caCert))
 			},
-			configureInfrastructure: configureTestInfrastructure,
+			configureInfrastructure: configureTestInfrastructure[*rsa.PrivateKey, *rsa.PublicKey],
 			configureOIDCServerBehaviour: func(t *testing.T, oidcServer *utilsoidc.TestServer, signingPrivateKey *rsa.PrivateKey) {
 				idTokenLifetime := time.Second * 1200
 				oidcServer.TokenHandler().EXPECT().Token().Times(1).DoAndReturn(utilsoidc.TokenHandlerBehaviorReturningPredefinedJWT(
@@ -720,7 +765,7 @@ jwt:
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			oidcServer, apiServer, signingPrivateKey, caCert, certPath := tt.configureInfrastructure(t, tt.authConfigFn)
+			oidcServer, apiServer, signingPrivateKey, caCert, certPath := tt.configureInfrastructure(t, tt.authConfigFn, rsaGenerateKey)
 
 			tt.configureOIDCServerBehaviour(t, oidcServer, signingPrivateKey)
 
@@ -743,10 +788,28 @@ jwt:
 	}
 }
 
-func configureTestInfrastructure(t *testing.T, fn authenticationConfigFunc) (
+func rsaGenerateKey(t *testing.T) (*rsa.PrivateKey, *rsa.PublicKey) {
+	t.Helper()
+
+	privateKey, err := rsa.GenerateKey(rand.Reader, rsaKeyBitSize)
+	require.NoError(t, err)
+
+	return privateKey, &privateKey.PublicKey
+}
+
+func ecdsaGenerateKey(t *testing.T) (*ecdsa.PrivateKey, *ecdsa.PublicKey) {
+	t.Helper()
+
+	privateKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	require.NoError(t, err)
+
+	return privateKey, &privateKey.PublicKey
+}
+
+func configureTestInfrastructure[K utilsoidc.JosePrivateKey, L utilsoidc.JosePublicKey](t *testing.T, fn authenticationConfigFunc, keyFunc func(t *testing.T) (K, L)) (
 	oidcServer *utilsoidc.TestServer,
 	apiServer *kubeapiserverapptesting.TestServer,
-	signingPrivateKey *rsa.PrivateKey,
+	signingPrivateKey K,
 	caCertContent []byte,
 	caFilePath string,
 ) {
@@ -754,19 +817,18 @@ func configureTestInfrastructure(t *testing.T, fn authenticationConfigFunc) (
 
 	caCertContent, _, caFilePath, caKeyFilePath := generateCert(t)
 
-	signingPrivateKey, err := rsa.GenerateKey(rand.Reader, rsaKeyBitSize)
-	require.NoError(t, err)
+	signingPrivateKey, publicKey := keyFunc(t)
 
 	oidcServer = utilsoidc.BuildAndRunTestServer(t, caFilePath, caKeyFilePath)
 
 	authenticationConfig := fn(t, oidcServer.URL(), string(caCertContent))
 	if len(authenticationConfig) > 0 {
-		apiServer = startTestAPIServerForOIDC(t, "", "", "", authenticationConfig)
+		apiServer = startTestAPIServerForOIDC(t, "", "", "", authenticationConfig, publicKey)
 	} else {
-		apiServer = startTestAPIServerForOIDC(t, oidcServer.URL(), defaultOIDCClientID, caFilePath, "")
+		apiServer = startTestAPIServerForOIDC(t, oidcServer.URL(), defaultOIDCClientID, caFilePath, "", publicKey)
 	}
 
-	oidcServer.JwksHandler().EXPECT().KeySet().AnyTimes().DoAndReturn(utilsoidc.DefaultJwksHandlerBehavior(t, &signingPrivateKey.PublicKey))
+	oidcServer.JwksHandler().EXPECT().KeySet().AnyTimes().DoAndReturn(utilsoidc.DefaultJwksHandlerBehavior(t, publicKey))
 
 	adminClient := kubernetes.NewForConfigOrDie(apiServer.ClientConfig)
 	configureRBAC(t, adminClient, defaultRole, defaultRoleBinding)
@@ -815,7 +877,7 @@ func configureClientConfigForOIDC(t *testing.T, config *rest.Config, clientID, c
 	return cfg
 }
 
-func startTestAPIServerForOIDC(t *testing.T, oidcURL, oidcClientID, oidcCAFilePath, authenticationConfigYAML string) *kubeapiserverapptesting.TestServer {
+func startTestAPIServerForOIDC[L utilsoidc.JosePublicKey](t *testing.T, oidcURL, oidcClientID, oidcCAFilePath, authenticationConfigYAML string, publicKey L) *kubeapiserverapptesting.TestServer {
 	t.Helper()
 
 	var customFlags []string
@@ -828,6 +890,7 @@ func startTestAPIServerForOIDC(t *testing.T, oidcURL, oidcClientID, oidcCAFilePa
 			fmt.Sprintf("--oidc-ca-file=%s", oidcCAFilePath),
 			fmt.Sprintf("--oidc-username-prefix=%s", defaultOIDCUsernamePrefix),
 		}
+		customFlags = append(customFlags, maybeSetSigningAlgs(publicKey)...)
 	}
 	customFlags = append(customFlags, "--authorization-mode=RBAC")
 
@@ -844,6 +907,18 @@ func startTestAPIServerForOIDC(t *testing.T, oidcURL, oidcClientID, oidcCAFilePa
 	return &server
 }
 
+func maybeSetSigningAlgs[K utilsoidc.JoseKey](key K) []string {
+	alg := utilsoidc.GetSignatureAlgorithm(key)
+	if alg == jose.RS256 && randomBool() {
+		return nil // check the default case of RS256 by not always setting the flag
+	}
+	return []string{
+		fmt.Sprintf("--oidc-signing-algs=%s", alg), // all other algs need to be manually set
+	}
+}
+
+func randomBool() bool { return utilrand.Int()%2 == 1 }
+
 func fetchOIDCCredentials(t *testing.T, oidcTokenURL string, caCertContent []byte) (idToken, refreshToken string) {
 	t.Helper()
 

test/utils/oidc/testserver.go

@@ -18,6 +18,7 @@ package oidc
 
 import (
 	"crypto"
+	"crypto/ecdsa"
 	"crypto/rsa"
 	"crypto/tls"
 	"encoding/hex"
@@ -170,17 +171,21 @@ func BuildAndRunTestServer(t *testing.T, caPath, caKeyPath string) *TestServer {
 	return oidcServer
 }
 
+type JosePrivateKey interface {
+	*rsa.PrivateKey | *ecdsa.PrivateKey
+}
+
 // TokenHandlerBehaviorReturningPredefinedJWT describes the scenario when signed JWT token is being created.
 // This behavior should being applied to the MockTokenHandler.
-func TokenHandlerBehaviorReturningPredefinedJWT(
+func TokenHandlerBehaviorReturningPredefinedJWT[K JosePrivateKey](
 	t *testing.T,
-	rsaPrivateKey *rsa.PrivateKey,
+	privateKey K,
 	claims map[string]interface{}, accessToken, refreshToken string,
 ) func() (Token, error) {
 	t.Helper()
 
 	return func() (Token, error) {
-		signer, err := jose.NewSigner(jose.SigningKey{Algorithm: jose.RS256, Key: rsaPrivateKey}, nil)
+		signer, err := jose.NewSigner(jose.SigningKey{Algorithm: GetSignatureAlgorithm(privateKey), Key: privateKey}, nil)
 		require.NoError(t, err)
 
 		payloadJSON, err := json.Marshal(claims)
@@ -199,13 +204,17 @@ func TokenHandlerBehaviorReturningPredefinedJWT(
 	}
 }
 
+type JosePublicKey interface {
+	*rsa.PublicKey | *ecdsa.PublicKey
+}
+
 // DefaultJwksHandlerBehavior describes the scenario when JSON Web Key Set token is being returned.
 // This behavior should being applied to the MockJWKsHandler.
-func DefaultJwksHandlerBehavior(t *testing.T, verificationPublicKey *rsa.PublicKey) func() jose.JSONWebKeySet {
+func DefaultJwksHandlerBehavior[K JosePublicKey](t *testing.T, verificationPublicKey K) func() jose.JSONWebKeySet {
 	t.Helper()
 
 	return func() jose.JSONWebKeySet {
-		key := jose.JSONWebKey{Key: verificationPublicKey, Use: "sig", Algorithm: string(jose.RS256)}
+		key := jose.JSONWebKey{Key: verificationPublicKey, Use: "sig", Algorithm: string(GetSignatureAlgorithm(verificationPublicKey))}
 
 		thumbprint, err := key.Thumbprint(crypto.SHA256)
 		require.NoError(t, err)
@@ -216,3 +225,16 @@ func DefaultJwksHandlerBehavior(t *testing.T, verificationPublicKey *rsa.PublicK
 		}
 	}
 }
+
+type JoseKey interface{ JosePrivateKey | JosePublicKey }
+
+func GetSignatureAlgorithm[K JoseKey](key K) jose.SignatureAlgorithm {
+	switch any(key).(type) {
+	case *rsa.PrivateKey, *rsa.PublicKey:
+		return jose.RS256
+	case *ecdsa.PrivateKey, *ecdsa.PublicKey:
+		return jose.ES256
+	default:
+		panic("unknown key type") // should be impossible
+	}
+}