Fixes for SPR-16624

Fixes: gh-5164

test/src/main/java/org/springframework/security/test/web/servlet/request/SecurityMockMvcRequestBuilders.java

@@ -90,6 +90,7 @@ public final class SecurityMockMvcRequestBuilders {
 		@Override
 		public MockHttpServletRequest buildRequest(ServletContext servletContext) {
 			MockHttpServletRequest request = post(this.logoutUrl)
+					.accept(MediaType.TEXT_HTML, MediaType.ALL)
 					.buildRequest(servletContext);
 			return this.postProcessor.postProcessRequest(request);
 		}

test/src/test/java/org/springframework/security/test/web/servlet/showcase/login/AuthenticationTests.java

@@ -27,6 +27,7 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;
+import org.springframework.http.MediaType;
 import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
 import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
 import org.springframework.security.core.userdetails.User;
@@ -53,7 +54,10 @@ public class AuthenticationTests {
 
 	@Before
 	public void setup() {
-		mvc = MockMvcBuilders.webAppContextSetup(context).apply(springSecurity()).build();
+		mvc = MockMvcBuilders.webAppContextSetup(context)
+				.apply(springSecurity())
+				.defaultRequest(get("/").accept(MediaType.TEXT_HTML))
+				.build();
 	}
 
 	@Test