Make sure bean resolver is set in the OAuth2 expression evaluator

Also copies the ExpressionParser (the only public getter), trust
resolver and permission evaluator (if available in the context). Changes
the logic to not replace an existing OAuth2MethodSecurityExpressionHandler
so that users can override simply by providing a bean of that type.

Fixes gh-3542

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/oauth2/method/OAuth2MethodSecurityConfiguration.java

@@ -17,13 +17,18 @@
 package org.springframework.boot.autoconfigure.security.oauth2.method;
 
 import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanFactoryUtils;
 import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
 import org.springframework.beans.factory.config.BeanPostProcessor;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationContextAware;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.security.access.PermissionEvaluator;
 import org.springframework.security.access.expression.method.DefaultMethodSecurityExpressionHandler;
+import org.springframework.security.authentication.AuthenticationTrustResolver;
 import org.springframework.security.config.annotation.method.configuration.GlobalMethodSecurityConfiguration;
 import org.springframework.security.oauth2.common.OAuth2AccessToken;
 import org.springframework.security.oauth2.provider.expression.OAuth2MethodSecurityExpressionHandler;
@@ -39,18 +44,35 @@ import org.springframework.security.oauth2.provider.expression.OAuth2MethodSecur
 @Configuration
 @ConditionalOnClass({ OAuth2AccessToken.class })
 @ConditionalOnBean(GlobalMethodSecurityConfiguration.class)
-public class OAuth2MethodSecurityConfiguration implements BeanFactoryPostProcessor {
+public class OAuth2MethodSecurityConfiguration implements BeanFactoryPostProcessor,
+		ApplicationContextAware {
+
+	private ApplicationContext applicationContext;
+
+	@Override
+	public void setApplicationContext(ApplicationContext applicationContext)
+			throws BeansException {
+		this.applicationContext = applicationContext;
+	}
 
 	@Override
 	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
 			throws BeansException {
-		OAuth2ExpressionHandlerInjectionPostProcessor processor = new OAuth2ExpressionHandlerInjectionPostProcessor();
+		OAuth2ExpressionHandlerInjectionPostProcessor processor = new OAuth2ExpressionHandlerInjectionPostProcessor(
+				this.applicationContext);
 		beanFactory.addBeanPostProcessor(processor);
 	}
 
 	private static class OAuth2ExpressionHandlerInjectionPostProcessor implements
 			BeanPostProcessor {
 
+		private ApplicationContext applicationContext;
+
+		public OAuth2ExpressionHandlerInjectionPostProcessor(
+				ApplicationContext applicationContext) {
+			this.applicationContext = applicationContext;
+		}
+
 		@Override
 		public Object postProcessBeforeInitialization(Object bean, String beanName)
 				throws BeansException {
@@ -60,11 +82,36 @@ public class OAuth2MethodSecurityConfiguration implements BeanFactoryPostProcess
 		@Override
 		public Object postProcessAfterInitialization(Object bean, String beanName)
 				throws BeansException {
-			if (bean instanceof DefaultMethodSecurityExpressionHandler) {
-				return new OAuth2MethodSecurityExpressionHandler();
+			if (bean instanceof DefaultMethodSecurityExpressionHandler
+					&& !(bean instanceof OAuth2MethodSecurityExpressionHandler)) {
+				return getExpressionHandler((DefaultMethodSecurityExpressionHandler) bean);
 			}
 			return bean;
 		}
+
+		private OAuth2MethodSecurityExpressionHandler getExpressionHandler(
+				DefaultMethodSecurityExpressionHandler bean) {
+			OAuth2MethodSecurityExpressionHandler handler = new OAuth2MethodSecurityExpressionHandler();
+			handler.setApplicationContext(this.applicationContext);
+			AuthenticationTrustResolver trustResolver = findInContext(AuthenticationTrustResolver.class);
+			if (trustResolver != null) {
+				handler.setTrustResolver(trustResolver);
+			}
+			PermissionEvaluator permissions = findInContext(PermissionEvaluator.class);
+			if (permissions != null) {
+				handler.setPermissionEvaluator(permissions);
+			}
+			handler.setExpressionParser(bean.getExpressionParser());
+			return handler;
+		}
+
+		private <T> T findInContext(Class<T> type) {
+			if (BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
+					this.applicationContext, type).length == 1) {
+				return this.applicationContext.getBean(type);
+			}
+			return null;
+		}
 	}
 
 }