docs: add CurrentSecurityContext section and link references

Signed-off-by: songhee <songhee9327@gmail.com>

Author: soooii

docs/modules/ROOT/pages/servlet/authentication/anonymous.adoc

@@ -137,7 +137,8 @@ fun method(authentication: Authentication?): String {
 will always return "not anonymous", even for anonymous requests.
 The reason is that Spring MVC resolves the parameter using `HttpServletRequest#getPrincipal`, which is `null` when the request is anonymous.
 
-If you'd like to obtain the `Authentication` in anonymous requests, use `@CurrentSecurityContext` instead:
+If you'd like to obtain the `Authentication` in anonymous requests, use
+xref:servlet/integrations/mvc.adoc#mvc-current-security-context[`@CurrentSecurityContext`] instead:
 
 .Use CurrentSecurityContext for Anonymous requests
 [tabs]

docs/modules/ROOT/pages/servlet/authentication/architecture.adoc

@@ -97,7 +97,11 @@ val authorities = authentication.authorities
 ----
 ======
 
-// FIXME: Add links to and relevant description of HttpServletRequest.getRemoteUser() and @CurrentSecurityContext @AuthenticationPrincipal
+In Spring MVC, you can resolve the current principal with
+xref:servlet/integrations/mvc.adoc#mvc-authentication-principal[`@AuthenticationPrincipal`]
+and the full `SecurityContext` with
+xref:servlet/integrations/mvc.adoc#mvc-current-security-context[`@CurrentSecurityContext`].
+For Servlet API access, use `HttpServletRequest#getRemoteUser`.
 
 By default, `SecurityContextHolder` uses a `ThreadLocal` to store these details, which means that the `SecurityContext` is always available to methods in the same thread, even if the `SecurityContext` is not explicitly passed around as an argument to those methods.
 Using a `ThreadLocal` in this way is quite safe if you take care to clear the thread after the present principal's request is processed.

docs/modules/ROOT/pages/servlet/integrations/mvc.adoc

@@ -624,6 +624,72 @@ open fun findMessagesForUser(@CurrentUser("user_id") userId: String?): ModelAndV
 ----
 ======
 
+[[mvc-current-security-context]]
+== @CurrentSecurityContext
+
+Spring Security provides `CurrentSecurityContextArgumentResolver`, which can automatically resolve the current `SecurityContext` for Spring MVC arguments.
+By using `@EnableWebSecurity`, you automatically have this added to your Spring MVC configuration.
+If you use XML-based configuration, you must add this yourself:
+
+[source,xml]
+----
+<mvc:annotation-driven>
+		<mvc:argument-resolvers>
+				<bean class="org.springframework.security.web.method.annotation.CurrentSecurityContextArgumentResolver" />
+		</mvc:argument-resolvers>
+</mvc:annotation-driven>
+----
+
+Once `CurrentSecurityContextArgumentResolver` is configured, you can access the `SecurityContext` directly:
+
+[tabs]
+======
+Java::
++
+[source,java,role="primary"]
+----
+@GetMapping("/me")
+public String me(@CurrentSecurityContext SecurityContext context) {
+	return context.getAuthentication().getName();
+}
+----
+
+Kotlin::
++
+[source,kotlin,role="secondary"]
+----
+@GetMapping("/me")
+fun me(@CurrentSecurityContext context: SecurityContext): String {
+    return context.authentication.name
+}
+----
+======
+
+You can also use a SpEL expression that is rooted at the `SecurityContext`:
+
+[tabs]
+======
+Java::
++
+[source,java,role="primary"]
+----
+@GetMapping("/me")
+public String me(@CurrentSecurityContext(expression = "authentication") Authentication authentication) {
+	return authentication.getName();
+}
+----
+
+Kotlin::
++
+[source,kotlin,role="secondary"]
+----
+@GetMapping("/me")
+fun me(@CurrentSecurityContext(expression = "authentication") authentication: Authentication): String {
+    return authentication.name
+}
+----
+======
+
 [[mvc-async]]
 == Spring MVC Async Integration