Support add nested security configurers during builder initialization

Closes gh-17011

Signed-off-by: DingHao <dh.hiekn@gmail.com>

Author: kse-music

config/src/main/java/org/springframework/security/config/annotation/AbstractConfiguredSecurityBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -49,6 +49,7 @@
  * @param <O> The object that this builder returns
  * @param <B> The type of this builder (that is returned by the base class)
  * @author Rob Winch
+ * @author DingHao
  * @see WebSecurity
  */
 public abstract class AbstractConfiguredSecurityBuilder<O, B extends SecurityBuilder<O>>
@@ -364,8 +365,10 @@ private void init() throws Exception {
 		for (SecurityConfigurer<O, B> configurer : configurers) {
 			configurer.init((B) this);
 		}
-		for (SecurityConfigurer<O, B> configurer : this.configurersAddedInInitializing) {
-			configurer.init((B) this);
+		while (!this.configurersAddedInInitializing.isEmpty()) {
+			for (SecurityConfigurer<O, B> configurer : getConfigurersInInitializing()) {
+				configurer.init((B) this);
+			}
 		}
 	}
 
@@ -385,6 +388,12 @@ private Collection<SecurityConfigurer<O, B>> getConfigurers() {
 		return result;
 	}
 
+	private List<SecurityConfigurer<O, B>> getConfigurersInInitializing() {
+		List<SecurityConfigurer<O, B>> result = new ArrayList<>(this.configurersAddedInInitializing);
+		this.configurersAddedInInitializing.clear();
+		return result;
+	}
+
 	/**
 	 * Determines if the object is unbuilt.
 	 * @return true, if unbuilt else false

config/src/test/java/org/springframework/security/config/annotation/web/AbstractConfiguredSecurityBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -163,6 +163,34 @@ public void withWhenDuplicateConfigurerAddedThenDuplicateConfigurerRemoved() thr
 		assertThat(this.builder.getConfigurers(TestSecurityConfigurer.class)).hasSize(1);
 	}
 
+	@Test
+	public void withWhenConfigurerAddInitializing() throws Exception {
+		this.builder.with(new FooConfigurer(), Customizer.withDefaults());
+		assertThat(this.builder.build()).isEqualTo("success");
+	}
+
+	private static class FooConfigurer extends SecurityConfigurerAdapter<Object, TestConfiguredSecurityBuilder> {
+
+		@Override
+		public void init(TestConfiguredSecurityBuilder builder) throws Exception {
+			builder.with(new BarConfigurer(), Customizer.withDefaults());
+		}
+
+	}
+
+	private static class BarConfigurer extends SecurityConfigurerAdapter<Object, TestConfiguredSecurityBuilder> {
+
+		@Override
+		public void init(TestConfiguredSecurityBuilder http) throws Exception {
+			http.with(new CooConfigurer(), Customizer.withDefaults());
+		}
+
+	}
+
+	private static class CooConfigurer extends SecurityConfigurerAdapter<Object, TestConfiguredSecurityBuilder> {
+
+	}
+
 	private static class ApplyAndRemoveSecurityConfigurer
 			extends SecurityConfigurerAdapter<Object, TestConfiguredSecurityBuilder> {