Support nested builder in DSL for reactive apps

Fixes: gh-7107

samples/boot/webflux-form/src/main/java/sample/WebfluxFormSecurityConfig.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -24,6 +24,8 @@ import org.springframework.security.core.userdetails.User;
 import org.springframework.security.core.userdetails.UserDetails;
 import org.springframework.security.web.server.SecurityWebFilterChain;
 
+import static org.springframework.security.config.Customizer.withDefaults;
+
 /**
  * @author Rob Winch
  * @since 5.0
@@ -42,15 +44,18 @@ public class WebfluxFormSecurityConfig {
 	}
 
 	@Bean
-	SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) {
+	SecurityWebFilterChain springSecurityFilterChain(ServerHttpSecurity http) throws Exception {
 		http
-			.authorizeExchange()
-				.pathMatchers("/login").permitAll()
-				.anyExchange().authenticated()
-				.and()
-			.httpBasic().and()
-			.formLogin()
-				.loginPage("/login");
+			.authorizeExchange(exchanges ->
+				exchanges
+					.pathMatchers("/login").permitAll()
+					.anyExchange().authenticated()
+			)
+			.httpBasic(withDefaults())
+			.formLogin(formLogin ->
+				formLogin
+					.loginPage("/login")
+			);
 		return http.build();
 	}
 }