Polish Document Defer load CsrfToken

Issue gh-12105

Author: rwinch

docs/modules/ROOT/pages/migration.adoc

@@ -71,6 +71,60 @@ open fun springSecurity(http: HttpSecurity): SecurityFilterChain {
 ----
 ====
 
+If this breaks your application, then you can explicitly opt into the 5.8 defaults using the following configuration:
+
+.Defer Loading `CsrfToken`
+====
+.Java
+[source,java,role="primary"]
+----
+@Bean
+DefaultSecurityFilterChain springSecurity(HttpSecurity http) throws Exception {
+	CsrfTokenRequestAttributeHandler requestHandler = new CsrfTokenRequestAttributeHandler();
+	// set the name of the attribute the CsrfToken will be populated on
+	requestHandler.setCsrfRequestAttributeName(null);
+	http
+		// ...
+		.csrf((csrf) -> csrf
+			.csrfTokenRequestHandler(requestHandler)
+		);
+	return http.build();
+}
+----
+
+.Kotlin
+[source,kotlin,role="secondary"]
+----
+@Bean
+open fun springSecurity(http: HttpSecurity): SecurityFilterChain {
+	val requestHandler = CsrfTokenRequestAttributeHandler()
+	// set the name of the attribute the CsrfToken will be populated on
+	requestHandler.setCsrfRequestAttributeName(null)
+	http {
+		csrf {
+			csrfTokenRequestHandler = requestHandler
+		}
+	}
+	return http.build()
+}
+----
+
+.XML
+[source,xml,role="secondary"]
+----
+<http>
+	<!-- ... -->
+	<csrf request-handler-ref="requestHandler"/>
+</http>
+<b:bean id="requestHandler"
+	class="org.springframework.security.web.csrf.CsrfTokenRequestAttributeHandler">
+	<b:property name="csrfRequestAttributeName">
+		<b:null/>
+	</b:property>
+</b:bean>
+----
+====
+
 === Explicit Save SecurityContextRepository
 
 In Spring Security 5, the default behavior is for the xref:servlet/authentication/architecture.adoc#servlet-authentication-securitycontext[`SecurityContext`] to automatically be saved to the xref:servlet/authentication/persistence.adoc#securitycontextrepository[`SecurityContextRepository`] using the xref:servlet/authentication/persistence.adoc#securitycontextpersistencefilter[`SecurityContextPersistenceFilter`].