Bug 1942915: pkg/.../create_error_template: fix error page template

Author: s-urbaniak

modules/customizing-the-login-page.adoc

@@ -11,6 +11,11 @@ Google, to show users a branded page that they trust and expect before being
 redirected to the authentication provider. You can also render custom error
 pages during the authentication process.
 
+[NOTE]
+====
+Customizing the error template is limited to identity providers (IDPs) that use redirects, such as request header and OIDC-based IDPs. It does not have an effect on IDPs that use direct password authentication, such as LDAP and HTPasswd.
+====
+
 .Prerequisites
 
 * You must have administrator privileges.