Default resolution of non-annotated Principal argument

Closes gh-25981

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/PrincipalMethodArgumentResolverTests.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright 2002-2020 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.mvc.method.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.lang.reflect.Method;
+import java.security.Principal;
+
+import javax.servlet.ServletRequest;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.method.support.ModelAndViewContainer;
+import org.springframework.web.testfixture.servlet.MockHttpServletRequest;
+import org.springframework.web.testfixture.servlet.MockHttpServletResponse;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link PrincipalMethodArgumentResolver}.
+ *
+ * @author Rossen Stoyanchev
+ */
+public class PrincipalMethodArgumentResolverTests {
+
+	private PrincipalMethodArgumentResolver resolver;
+
+	private ModelAndViewContainer mavContainer;
+
+	private MockHttpServletRequest servletRequest;
+
+	private ServletWebRequest webRequest;
+
+	private Method method;
+
+
+	@BeforeEach
+	public void setup() throws Exception {
+		resolver = new PrincipalMethodArgumentResolver();
+		mavContainer = new ModelAndViewContainer();
+		servletRequest = new MockHttpServletRequest("GET", "");
+		webRequest = new ServletWebRequest(servletRequest, new MockHttpServletResponse());
+
+		method = getClass().getMethod("supportedParams", ServletRequest.class, Principal.class);
+	}
+
+
+	@Test
+	public void principal() throws Exception {
+		Principal principal = () -> "Foo";
+		servletRequest.setUserPrincipal(principal);
+
+		MethodParameter principalParameter = new MethodParameter(method, 1);
+		assertThat(resolver.supportsParameter(principalParameter)).as("Principal not supported").isTrue();
+
+		Object result = resolver.resolveArgument(principalParameter, null, webRequest, null);
+		assertThat(result).as("Invalid result").isSameAs(principal);
+	}
+
+	@Test
+	public void principalAsNull() throws Exception {
+		MethodParameter principalParameter = new MethodParameter(method, 1);
+		assertThat(resolver.supportsParameter(principalParameter)).as("Principal not supported").isTrue();
+
+		Object result = resolver.resolveArgument(principalParameter, null, webRequest, null);
+		assertThat(result).as("Invalid result").isNull();
+	}
+
+	@Test // gh-25780
+	public void annotatedPrincipal() throws Exception {
+		Principal principal = () -> "Foo";
+		servletRequest.setUserPrincipal(principal);
+		Method principalMethod = getClass().getMethod("supportedParamsWithAnnotatedPrincipal", Principal.class);
+
+		MethodParameter principalParameter = new MethodParameter(principalMethod, 0);
+		assertThat(resolver.supportsParameter(principalParameter)).isTrue();
+	}
+
+
+	@SuppressWarnings("unused")
+	public void supportedParams(ServletRequest p0, Principal p1) {}
+
+	@Target({ ElementType.PARAMETER })
+	@Retention(RetentionPolicy.RUNTIME)
+	public @interface AuthenticationPrincipal {}
+
+	@SuppressWarnings("unused")
+	public void supportedParamsWithAnnotatedPrincipal(@AuthenticationPrincipal Principal p) {}
+
+}