Add direct WebFlux and WebMvc endpoint support

Add `@ControllerEndpoint` and `@RestControllerEndpoint` annotations that
can be used to develop a Spring-only request mapped endpoint. Both
Spring MVC and Spring WebFlux are supported.

This feature is primarily for use when deeper Spring integration is
required or when existing Spring Boot 1.5 projects want to migrate to
Spring Boot 2.0 without re-writing existing endpoints. It comes at the
expense of portability, since such endpoints will be missing from
Jersey.

Fixes gh-10257

spring-boot-samples/spring-boot-sample-actuator-custom-security/src/main/java/sample/actuator/customsecurity/ExampleRestControllerEndpoint.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2012-2018 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
+ *
+ *      http://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 sample.actuator.customsecurity;
+
+import org.springframework.boot.actuate.endpoint.web.annotation.RestControllerEndpoint;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Component;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+
+@Component
+@RestControllerEndpoint(id = "example")
+public class ExampleRestControllerEndpoint {
+
+	@GetMapping("/echo")
+	public ResponseEntity<String> echo(@RequestParam("text") String text) {
+		return ResponseEntity.ok().header("echo", text).body(text);
+	}
+
+}

spring-boot-samples/spring-boot-sample-actuator-custom-security/src/test/java/sample/actuator/customsecurity/SampleActuatorCustomSecurityApplicationTests.java

@@ -109,6 +109,22 @@ public class SampleActuatorCustomSecurityApplicationTests {
 		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.UNAUTHORIZED);
 	}
 
+	@Test
+	public void actuatorCustomMvcSecureEndpointWithUnauthorizedUser() {
+		ResponseEntity<String> entity = userRestTemplate()
+				.getForEntity("/actuator/example/echo?text={t}", String.class, "test");
+		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.FORBIDDEN);
+	}
+
+	@Test
+	public void actuatorCustomMvcSecureEndpointWithAuthorizedUser() {
+		ResponseEntity<String> entity = adminRestTemplate()
+				.getForEntity("/actuator/example/echo?text={t}", String.class, "test");
+		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(entity.getBody()).isEqualTo("test");
+		assertThat(entity.getHeaders().getFirst("echo")).isEqualTo("test");
+	}
+
 	private TestRestTemplate restTemplate() {
 		return configure(new TestRestTemplate());
 	}