diff --git a/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/registration/ClientRegistrations.java b/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/registration/ClientRegistrations.java
index 6053681364..1f2d3f61c5 100644
--- a/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/registration/ClientRegistrations.java
+++ b/oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/registration/ClientRegistrations.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -239,8 +239,7 @@ public final class ClientRegistrations {
 				() -> "The Issuer \"" + metadataIssuer + "\" provided in the configuration metadata did "
 						+ "not match the requested issuer \"" + issuer + "\"");
 		String name = URI.create(issuer).getHost();
-		ClientAuthenticationMethod method = getClientAuthenticationMethod(issuer,
-				metadata.getTokenEndpointAuthMethods());
+		ClientAuthenticationMethod method = getClientAuthenticationMethod(metadata.getTokenEndpointAuthMethods());
 		Map<String, Object> configurationMetadata = new LinkedHashMap<>(metadata.toJSONObject());
 		// @formatter:off
 		return ClientRegistration.withRegistrationId(name)
@@ -256,7 +255,7 @@ public final class ClientRegistrations {
 		// @formatter:on
 	}
 
-	private static ClientAuthenticationMethod getClientAuthenticationMethod(String issuer,
+	private static ClientAuthenticationMethod getClientAuthenticationMethod(
 			List<com.nimbusds.oauth2.sdk.auth.ClientAuthenticationMethod> metadataAuthMethods) {
 		if (metadataAuthMethods == null || metadataAuthMethods
 				.contains(com.nimbusds.oauth2.sdk.auth.ClientAuthenticationMethod.CLIENT_SECRET_BASIC)) {
@@ -269,10 +268,7 @@ public final class ClientRegistrations {
 		if (metadataAuthMethods.contains(com.nimbusds.oauth2.sdk.auth.ClientAuthenticationMethod.NONE)) {
 			return ClientAuthenticationMethod.NONE;
 		}
-		throw new IllegalArgumentException(
-				"Only ClientAuthenticationMethod.CLIENT_SECRET_BASIC, ClientAuthenticationMethod.CLIENT_SECRET_POST and "
-						+ "ClientAuthenticationMethod.NONE are supported. The issuer \"" + issuer
-						+ "\" returned a configuration of " + metadataAuthMethods);
+		return null;
 	}
 
 	private interface ThrowingFunction<S, T, E extends Throwable> {
diff --git a/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/registration/ClientRegistrationsTests.java b/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/registration/ClientRegistrationsTests.java
index 0c809d3cdd..13e934e1bd 100644
--- a/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/registration/ClientRegistrationsTests.java
+++ b/oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/registration/ClientRegistrationsTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -298,6 +298,24 @@ public class ClientRegistrationsTests {
 				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
 	}
 
+	// gh-9780
+	@Test
+	public void issuerWhenClientSecretBasicAuthMethodThenMethodIsBasic() throws Exception {
+		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("client_secret_basic"));
+		ClientRegistration registration = registration("").build();
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
+	}
+
+	// gh-9780
+	@Test
+	public void issuerWhenOAuth2ClientSecretBasicAuthMethodThenMethodIsBasic() throws Exception {
+		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("client_secret_basic"));
+		ClientRegistration registration = registrationOAuth2("", null).build();
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
+	}
+
 	@Test
 	public void issuerWhenTokenEndpointAuthMethodsPostThenMethodIsPost() throws Exception {
 		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("client_secret_post"));
@@ -314,6 +332,46 @@ public class ClientRegistrationsTests {
 				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_POST);
 	}
 
+	// gh-9780
+	@Test
+	public void issuerWhenClientSecretJwtAuthMethodThenMethodIsClientSecretBasic() throws Exception {
+		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("client_secret_jwt"));
+		ClientRegistration registration = registration("").build();
+		// The client_secret_basic auth method is still the default
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
+	}
+
+	// gh-9780
+	@Test
+	public void issuerWhenOAuth2ClientSecretJwtAuthMethodThenMethodIsClientSecretBasic() throws Exception {
+		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("client_secret_jwt"));
+		ClientRegistration registration = registrationOAuth2("", null).build();
+		// The client_secret_basic auth method is still the default
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
+	}
+
+	// gh-9780
+	@Test
+	public void issuerWhenPrivateKeyJwtAuthMethodThenMethodIsClientSecretBasic() throws Exception {
+		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("private_key_jwt"));
+		ClientRegistration registration = registration("").build();
+		// The client_secret_basic auth method is still the default
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
+	}
+
+	// gh-9780
+	@Test
+	public void issuerWhenOAuth2PrivateKeyJwtAuthMethodThenMethodIsClientSecretBasic() throws Exception {
+		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("private_key_jwt"));
+		ClientRegistration registration = registrationOAuth2("", null).build();
+		// The client_secret_basic auth method is still the default
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
+	}
+
 	@Test
 	public void issuerWhenTokenEndpointAuthMethodsNoneThenMethodIsNone() throws Exception {
 		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("none"));
@@ -328,32 +386,24 @@ public class ClientRegistrationsTests {
 		assertThat(registration.getClientAuthenticationMethod()).isEqualTo(ClientAuthenticationMethod.NONE);
 	}
 
-	/**
-	 * We currently only support client_secret_basic, so verify we have a meaningful error
-	 * until we add support.
-	 */
+	// gh-9780
 	@Test
-	public void issuerWhenTokenEndpointAuthMethodsInvalidThenException() {
+	public void issuerWhenTlsClientAuthMethodThenSuccess() throws Exception {
 		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("tls_client_auth"));
-		// @formatter:off
-		assertThatIllegalArgumentException()
-				.isThrownBy(() -> registration(""))
-				.withMessageContaining("Only ClientAuthenticationMethod.CLIENT_SECRET_BASIC, ClientAuthenticationMethod.CLIENT_SECRET_POST and "
-						+ "ClientAuthenticationMethod.NONE are supported. The issuer \"" + this.issuer
-						+ "\" returned a configuration of [tls_client_auth]");
-		// @formatter:on
+		ClientRegistration registration = registration("").build();
+		// The client_secret_basic auth method is still the default
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
 	}
 
+	// gh-9780
 	@Test
-	public void issuerWhenOAuth2TokenEndpointAuthMethodsInvalidThenException() {
+	public void issuerWhenOAuth2TlsClientAuthMethodThenSuccess() throws Exception {
 		this.response.put("token_endpoint_auth_methods_supported", Arrays.asList("tls_client_auth"));
-		// @formatter:off
-		assertThatIllegalArgumentException()
-				.isThrownBy(() -> registrationOAuth2("", null))
-				.withMessageContaining("Only ClientAuthenticationMethod.CLIENT_SECRET_BASIC, ClientAuthenticationMethod.CLIENT_SECRET_POST and "
-						+ "ClientAuthenticationMethod.NONE are supported. The issuer \"" + this.issuer
-						+ "\" returned a configuration of [tls_client_auth]");
-		// @formatter:on
+		ClientRegistration registration = registrationOAuth2("", null).build();
+		// The client_secret_basic auth method is still the default
+		assertThat(registration.getClientAuthenticationMethod())
+				.isEqualTo(ClientAuthenticationMethod.CLIENT_SECRET_BASIC);
 	}
 
 	@Test