Update HandlerMappingIntrospector Usage in CORS support

Closes spring-projectsgh-16501

Author: evgeniycheban

config/src/main/java/org/springframework/security/config/annotation/web/configurers/CorsConfigurer.java

@@ -24,6 +24,7 @@
 import org.springframework.util.ClassUtils;
 import org.springframework.web.cors.CorsConfiguration;
 import org.springframework.web.cors.CorsConfigurationSource;
+import org.springframework.web.cors.PreFlightRequestHandler;
 import org.springframework.web.filter.CorsFilter;
 import org.springframework.web.servlet.handler.HandlerMappingIntrospector;
 
@@ -110,11 +111,13 @@ private static CorsFilter getMvcCorsFilter(ApplicationContext context) {
 			if (!context.containsBean(HANDLER_MAPPING_INTROSPECTOR_BEAN_NAME)) {
 				throw new NoSuchBeanDefinitionException(HANDLER_MAPPING_INTROSPECTOR_BEAN_NAME, "A Bean named "
 						+ HANDLER_MAPPING_INTROSPECTOR_BEAN_NAME + " of type "
-						+ HandlerMappingIntrospector.class.getName()
+						+ PreFlightRequestHandler.class.getName()
 						+ " is required to use MvcRequestMatcher. Please ensure Spring Security & Spring MVC are configured in a shared ApplicationContext.");
 			}
-			HandlerMappingIntrospector mappingIntrospector = context.getBean(HANDLER_MAPPING_INTROSPECTOR_BEAN_NAME,
-					HandlerMappingIntrospector.class);
+			PreFlightRequestHandler mappingIntrospector = context.getBean(HANDLER_MAPPING_INTROSPECTOR_BEAN_NAME,
+					PreFlightRequestHandler.class);
+			Assert.isInstanceOf(CorsConfigurationSource.class, mappingIntrospector,
+					() -> "mappingIntrospector must implement " + CorsConfigurationSource.class.getName());
 			return new CorsFilter(mappingIntrospector);
 		}