Handle missing authorization endpoint uri

Closes gh-9795

oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/registration/ClientRegistrations.java

@@ -248,7 +248,7 @@ public final class ClientRegistrations {
 				.authorizationGrantType(AuthorizationGrantType.AUTHORIZATION_CODE)
 				.clientAuthenticationMethod(method)
 				.redirectUri("{baseUrl}/{action}/oauth2/code/{registrationId}")
-				.authorizationUri(metadata.getAuthorizationEndpointURI().toASCIIString())
+				.authorizationUri((metadata.getAuthorizationEndpointURI() != null) ? metadata.getAuthorizationEndpointURI().toASCIIString() : null)
 				.providerConfigurationMetadata(configurationMetadata)
 				.tokenUri(metadata.getTokenEndpointURI().toASCIIString())
 				.issuerUri(issuer)

oauth2/oauth2-client/src/test/java/org/springframework/security/oauth2/client/registration/ClientRegistrationsTests.java

@@ -258,6 +258,30 @@ public class ClientRegistrationsTests {
 		assertThat(registration.getAuthorizationGrantType()).isEqualTo(AuthorizationGrantType.AUTHORIZATION_CODE);
 	}
 
+	// gh-9795
+	@Test
+	public void issuerWhenResponseAuthorizationEndpointIsNullThenSuccess() throws Exception {
+		this.response.put("grant_types_supported", Arrays.asList("urn:ietf:params:oauth:grant-type:jwt-bearer"));
+		this.response.remove("authorization_endpoint");
+		ClientRegistration registration = registration("").authorizationGrantType(AuthorizationGrantType.JWT_BEARER)
+				.build();
+		assertThat(registration.getAuthorizationGrantType()).isEqualTo(AuthorizationGrantType.JWT_BEARER);
+		ClientRegistration.ProviderDetails provider = registration.getProviderDetails();
+		assertThat(provider.getAuthorizationUri()).isNull();
+	}
+
+	// gh-9795
+	@Test
+	public void issuerWhenOAuth2ResponseAuthorizationEndpointIsNullThenSuccess() throws Exception {
+		this.response.put("grant_types_supported", Arrays.asList("urn:ietf:params:oauth:grant-type:jwt-bearer"));
+		this.response.remove("authorization_endpoint");
+		ClientRegistration registration = registrationOAuth2("", null)
+				.authorizationGrantType(AuthorizationGrantType.JWT_BEARER).build();
+		assertThat(registration.getAuthorizationGrantType()).isEqualTo(AuthorizationGrantType.JWT_BEARER);
+		ClientRegistration.ProviderDetails provider = registration.getProviderDetails();
+		assertThat(provider.getAuthorizationUri()).isNull();
+	}
+
 	@Test
 	public void issuerWhenTokenEndpointAuthMethodsNullThenDefaulted() throws Exception {
 		this.response.remove("token_endpoint_auth_methods_supported");