Allow users to customize authentication entry point in OAuth2 SSO

The SsoSecurityConfigurer that gets added when a user has a custom
WebSecurityConfigurer with @EnableOAuth2Sso is quite opinionated, and
this is preventing users from custimizing the exception handling in the
customized UI security. This change makes it less opinionated, using
request matchers to configure the default instead of ovewriting the
single authentication entry point.

Also adds an entry point responding with a 401 for XHR clients (just like
the vanilla HTTP Basic auth).

Fixes gh-4629

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/security/oauth2/sso/BasicOAuth2SsoConfigurationTests.java

@@ -77,6 +77,12 @@ public class BasicOAuth2SsoConfigurationTests {
 				.andExpect(header().string("location", "http://localhost/login"));
 	}
 
+	@Test
+	public void homePageSends401ToXhr() throws Exception {
+		this.mvc.perform(get("/").header("X-Requested-With", "XMLHttpRequest"))
+				.andExpect(status().isUnauthorized());
+	}
+
 	@Configuration
 	@Import(OAuth2AutoConfiguration.class)
 	@EnableOAuth2Sso

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/security/oauth2/sso/CustomOAuth2SsoConfigurationTests.java

@@ -89,6 +89,12 @@ public class CustomOAuth2SsoConfigurationTests {
 				.andExpect(header().string("location", "http://localhost/login"));
 	}
 
+	@Test
+	public void uiPageSends401ToXhr() throws Exception {
+		this.mvc.perform(get("/ui/").header("X-Requested-With", "XMLHttpRequest"))
+				.andExpect(status().isUnauthorized());
+	}
+
 	@Test
 	public void uiTestPageIsAccessible() throws Exception {
 		this.mvc.perform(get("/ui/test")).andExpect(status().isOk())

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/security/oauth2/sso/CustomOAuth2SsoWithAuthenticationEntryPointConfigurationTests.java

@@ -0,0 +1,125 @@
+/*
+ * Copyright 2012-2015 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 org.springframework.boot.autoconfigure.security.oauth2.sso;
+
+import javax.servlet.Filter;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Qualifier;
+import org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration;
+import org.springframework.boot.autoconfigure.security.oauth2.client.EnableOAuth2Sso;
+import org.springframework.boot.autoconfigure.security.oauth2.sso.CustomOAuth2SsoWithAuthenticationEntryPointConfigurationTests.TestConfiguration;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Import;
+import org.springframework.http.HttpStatus;
+import org.springframework.security.config.annotation.web.builders.HttpSecurity;
+import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
+import org.springframework.security.web.authentication.HttpStatusEntryPoint;
+import org.springframework.test.context.TestPropertySource;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.web.WebAppConfiguration;
+import org.springframework.test.web.servlet.MockMvc;
+import org.springframework.test.web.servlet.setup.MockMvcBuilders;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.context.WebApplicationContext;
+
+import static org.hamcrest.Matchers.startsWith;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.content;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.header;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
+
+/**
+ * Tests for {@link OAuth2AutoConfiguration} with custom configuration.
+ *
+ * @author Dave Syer
+ */
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration(TestConfiguration.class)
+@WebAppConfiguration
+@TestPropertySource(properties = { "security.oauth2.client.clientId=client",
+		"security.oauth2.client.clientSecret=secret",
+		"security.oauth2.client.authorizationUri=http://example.com/oauth/authorize",
+		"security.oauth2.client.tokenUri=http://example.com/oauth/token",
+		"security.oauth2.resource.jwt.keyValue=SSSSHHH" })
+public class CustomOAuth2SsoWithAuthenticationEntryPointConfigurationTests {
+
+	@Autowired
+	private WebApplicationContext context;
+
+	@Autowired
+	@Qualifier("springSecurityFilterChain")
+	private Filter filter;
+
+	private MockMvc mvc;
+
+	@Before
+	public void init() {
+		this.mvc = MockMvcBuilders.webAppContextSetup(this.context)
+				.addFilters(this.filter).build();
+	}
+
+	@Test
+	public void homePageIsBasicAuth() throws Exception {
+		this.mvc.perform(get("/")).andExpect(status().isUnauthorized())
+				.andExpect(header().string("WWW-Authenticate", startsWith("Basic")));
+	}
+
+	@Test
+	public void uiPageIsSecure() throws Exception {
+		this.mvc.perform(get("/ui/")).andExpect(status().isUnauthorized());
+	}
+
+	@Test
+	public void uiTestPageIsAccessible() throws Exception {
+		this.mvc.perform(get("/ui/test")).andExpect(status().isOk())
+				.andExpect(content().string("test"));
+	}
+
+	@Configuration
+	@EnableOAuth2Sso
+	@Import(OAuth2AutoConfiguration.class)
+	@MinimalSecureWebConfiguration
+	protected static class TestConfiguration extends WebSecurityConfigurerAdapter {
+
+		@Override
+		public void configure(HttpSecurity http) throws Exception {
+			http.antMatcher("/ui/**").authorizeRequests().antMatchers("/ui/test")
+					.permitAll().anyRequest().authenticated().and().exceptionHandling()
+					.authenticationEntryPoint(
+							new HttpStatusEntryPoint(HttpStatus.UNAUTHORIZED));
+		}
+
+		@RestController
+		public static class TestController {
+
+			@RequestMapping("/ui/test")
+			public String test() {
+				return "test";
+			}
+
+		}
+
+	}
+
+}