Ignore synthetic methods when checking for duplicate annotations

Closes gh-13132

core/src/main/java/org/springframework/security/authorization/method/AuthorizationAnnotationUtils.java

@@ -17,6 +17,7 @@
 package org.springframework.security.authorization.method;
 
 import java.lang.annotation.Annotation;
+import java.lang.reflect.Executable;
 import java.lang.reflect.Method;
 
 import org.springframework.core.annotation.AnnotationConfigurationException;
@@ -96,6 +97,10 @@ final class AuthorizationAnnotationUtils {
 			Class<A> annotationType) {
 		boolean alreadyFound = false;
 		for (MergedAnnotation<Annotation> mergedAnnotation : mergedAnnotations) {
+			if (isSynthetic(mergedAnnotation.getSource())) {
+				continue;
+			}
+
 			if (mergedAnnotation.getType() == annotationType) {
 				if (alreadyFound) {
 					return true;
@@ -106,6 +111,14 @@ final class AuthorizationAnnotationUtils {
 		return false;
 	}
 
+	private static boolean isSynthetic(Object object) {
+		if (object instanceof Executable) {
+			return ((Executable) object).isSynthetic();
+		}
+
+		return false;
+	}
+
 	private AuthorizationAnnotationUtils() {
 
 	}

core/src/test/java/org/springframework/security/authorization/method/AuthorizationAnnotationUtilsTests.java

@@ -0,0 +1,39 @@
+package org.springframework.security.authorization.method;
+
+import java.lang.reflect.Method;
+import java.lang.reflect.Proxy;
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.security.access.prepost.PreAuthorize;
+
+import static org.assertj.core.api.Assertions.assertThatNoException;
+
+/**
+ * Tests for {@link AuthorizationAnnotationUtils}
+ */
+class AuthorizationAnnotationUtilsTests {
+
+	@Test // gh-13132
+	public void annotationsOnSyntheticMethodsShouldNotTriggerAnnotationConfigurationException()
+			throws NoSuchMethodException {
+		StringRepository proxy =
+				(StringRepository) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
+						new Class[] {StringRepository.class}, (p, m, args) -> null);
+		Method method = proxy.getClass().getDeclaredMethod("findAll");
+		assertThatNoException()
+				.isThrownBy(() -> AuthorizationAnnotationUtils.findUniqueAnnotation(method, PreAuthorize.class));
+	}
+
+	private interface BaseRepository<T> {
+
+		Iterable<T> findAll();
+	}
+
+	private interface StringRepository extends BaseRepository<String> {
+
+		@Override
+		@PreAuthorize("hasRole('someRole')")
+		List<String> findAll();
+	}
+}