Optimized login form - delegated CSRF token creation to thymeleaf

Also added additional test to verify behaviour.

Fixes gh-1039

spring-boot-samples/spring-boot-sample-web-secure/src/test/java/sample/ui/secure/SampleSecureApplicationTests.java

@@ -69,6 +69,18 @@ public class SampleSecureApplicationTests {
 				entity.getHeaders().getLocation().toString().endsWith(port + "/login"));
 	}
 
+	@Test
+	public void testLoginPage() throws Exception {
+		HttpHeaders headers = new HttpHeaders();
+		headers.setAccept(Arrays.asList(MediaType.TEXT_HTML));
+		ResponseEntity<String> entity = new TestRestTemplate().exchange(
+				"http://localhost:" + this.port + "/login", HttpMethod.GET, new HttpEntity<Void>(
+						headers), String.class);
+		assertEquals(HttpStatus.OK, entity.getStatusCode());
+		assertTrue("Wrong content:\n" + entity.getBody(),
+				entity.getBody().contains("_csrf"));
+	}
+
 	@Test
 	public void testLogin() throws Exception {
 		HttpHeaders headers = getHeaders();