Document Observability Support

Issue gh-10964

docs/modules/ROOT/pages/servlet/appendix/namespace/authentication-manager.adoc

@@ -27,6 +27,9 @@ This attribute allows you to define an alias name for the internal instance for
 If set to true, the AuthenticationManager will attempt to clear any credentials data in the returned Authentication object, once the user has been authenticated.
 Literally it maps to the `eraseCredentialsAfterAuthentication` property of the xref:servlet/authentication/architecture.adoc#servlet-authentication-providermanager[`ProviderManager`].
 
+[[nsa-authentication-manager-observation-registry-ref]]
+* **observation-registry-ref**
+A reference to the `ObservationRegistry` used for the `FilterChain` and related components
 
 [[nsa-authentication-manager-id]]
 * **id**

docs/modules/ROOT/pages/servlet/appendix/namespace/http.adoc

@@ -47,6 +47,9 @@ By default an `AffirmativeBased` implementation is used for with a `RoleVoter` a
 * **authentication-manager-ref**
 A reference to the `AuthenticationManager` used for the `FilterChain` created by this http element.
 
+[[nsa-http-observation-registry-ref]]
+* **observation-registry-ref**
+A reference to the `ObservationRegistry` used for the `FilterChain` and related components
 
 [[nsa-http-auto-config]]
 * **auto-config**

docs/modules/ROOT/pages/servlet/appendix/namespace/method-security.adoc

@@ -37,6 +37,10 @@ Defaults to "false".
 Specifies a SecurityContextHolderStrategy to use when retrieving the SecurityContext.
 Defaults to the value returned by SecurityContextHolder.getContextHolderStrategy().
 
+[[nsa-method-security-observation-registry-ref]]
+* **observation-registry-ref**
+A reference to the `ObservationRegistry` used for the `FilterChain` and related components
+
 [[nsa-method-security-children]]
 === Child Elements of <method-security>