X509 client certificate authentication triggers when client id is provided

Closes gh-1635

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/config/annotation/web/configurers/OAuth2ClientAuthenticationConfigurer.java

@@ -240,10 +240,10 @@ public final class OAuth2ClientAuthenticationConfigurer extends AbstractOAuth2Co
 		List<AuthenticationConverter> authenticationConverters = new ArrayList<>();
 
 		authenticationConverters.add(new JwtClientAssertionAuthenticationConverter());
-		authenticationConverters.add(new X509ClientCertificateAuthenticationConverter());
 		authenticationConverters.add(new ClientSecretBasicAuthenticationConverter());
 		authenticationConverters.add(new ClientSecretPostAuthenticationConverter());
 		authenticationConverters.add(new PublicClientAuthenticationConverter());
+		authenticationConverters.add(new X509ClientCertificateAuthenticationConverter());
 
 		return authenticationConverters;
 	}

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/OAuth2ClientAuthenticationFilter.java

@@ -114,10 +114,10 @@ public final class OAuth2ClientAuthenticationFilter extends OncePerRequestFilter
 		this.authenticationConverter = new DelegatingAuthenticationConverter(
 				Arrays.asList(
 						new JwtClientAssertionAuthenticationConverter(),
-						new X509ClientCertificateAuthenticationConverter(),
 						new ClientSecretBasicAuthenticationConverter(),
 						new ClientSecretPostAuthenticationConverter(),
-						new PublicClientAuthenticationConverter()));
+						new PublicClientAuthenticationConverter(),
+						new X509ClientCertificateAuthenticationConverter()));
 		// @formatter:on
 	}
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/X509ClientCertificateAuthenticationConverter.java

@@ -59,7 +59,11 @@ public final class X509ClientCertificateAuthenticationConverter implements Authe
 
 		// client_id (REQUIRED)
 		String clientId = parameters.getFirst(OAuth2ParameterNames.CLIENT_ID);
-		if (!StringUtils.hasText(clientId) || parameters.get(OAuth2ParameterNames.CLIENT_ID).size() != 1) {
+		if (!StringUtils.hasText(clientId)) {
+			return null;
+		}
+
+		if (parameters.get(OAuth2ParameterNames.CLIENT_ID).size() != 1) {
 			throw new OAuth2AuthenticationException(OAuth2ErrorCodes.INVALID_REQUEST);
 		}
 

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/config/annotation/web/configurers/OAuth2ClientCredentialsGrantTests.java

@@ -309,6 +309,28 @@ public class OAuth2ClientCredentialsGrantTests {
 		verify(jwtCustomizer).customize(any());
 	}
 
+	// gh-1635
+	@Test
+	public void requestWhenTokenRequestIncludesBasicClientCredentialsAndX509ClientCertificateThenTokenResponse()
+			throws Exception {
+		this.spring.register(AuthorizationServerConfiguration.class).autowire();
+
+		RegisteredClient registeredClient = TestRegisteredClients.registeredClient2().build();
+		this.registeredClientRepository.save(registeredClient);
+
+		this.mvc
+			.perform(post(DEFAULT_TOKEN_ENDPOINT_URI).with(x509(TestX509Certificates.DEMO_CLIENT_PKI_CERTIFICATE))
+				.param(OAuth2ParameterNames.GRANT_TYPE, AuthorizationGrantType.CLIENT_CREDENTIALS.getValue())
+				.param(OAuth2ParameterNames.SCOPE, "scope1 scope2")
+				.header(HttpHeaders.AUTHORIZATION,
+						"Basic " + encodeBasicAuth(registeredClient.getClientId(), registeredClient.getClientSecret())))
+			.andExpect(status().isOk())
+			.andExpect(jsonPath("$.access_token").isNotEmpty())
+			.andExpect(jsonPath("$.scope").value("scope1 scope2"));
+
+		verify(jwtCustomizer).customize(any());
+	}
+
 	@Test
 	public void requestWhenTokenEndpointCustomizedThenUsed() throws Exception {
 		this.spring.register(AuthorizationServerConfigurationCustomTokenEndpoint.class).autowire();
@@ -394,10 +416,10 @@ public class OAuth2ClientCredentialsGrantTests {
 		List<AuthenticationConverter> authenticationConverters = authenticationConvertersCaptor.getValue();
 		assertThat(authenticationConverters).allMatch((converter) -> converter == authenticationConverter
 				|| converter instanceof JwtClientAssertionAuthenticationConverter
-				|| converter instanceof X509ClientCertificateAuthenticationConverter
 				|| converter instanceof ClientSecretBasicAuthenticationConverter
 				|| converter instanceof ClientSecretPostAuthenticationConverter
-				|| converter instanceof PublicClientAuthenticationConverter);
+				|| converter instanceof PublicClientAuthenticationConverter
+				|| converter instanceof X509ClientCertificateAuthenticationConverter);
 
 		verify(authenticationProvider).authenticate(eq(clientPrincipal));
 

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/authentication/X509ClientCertificateAuthenticationConverterTests.java

@@ -58,14 +58,12 @@ public class X509ClientCertificateAuthenticationConverterTests {
 	}
 
 	@Test
-	public void convertWhenMissingClientIdThenInvalidRequestError() {
+	public void convertWhenMissingClientIdThenReturnNull() {
 		MockHttpServletRequest request = new MockHttpServletRequest();
 		request.setAttribute("jakarta.servlet.request.X509Certificate",
 				TestX509Certificates.DEMO_CLIENT_PKI_CERTIFICATE);
-		assertThatThrownBy(() -> this.converter.convert(request)).isInstanceOf(OAuth2AuthenticationException.class)
-			.extracting((ex) -> ((OAuth2AuthenticationException) ex).getError())
-			.extracting("errorCode")
-			.isEqualTo(OAuth2ErrorCodes.INVALID_REQUEST);
+		Authentication authentication = this.converter.convert(request);
+		assertThat(authentication).isNull();
 	}
 
 	@Test