Add security warning for anonymous users setting

Author: jdiehl

content/en/docs/refguide/modeling/security/app-security/anonymous-users.md

@@ -21,6 +21,10 @@ The properties of anonymous users are described in the table below:
 | Allow anonymous users | When **Yes** is selected, anonymous users are allowed. End-users do not have to sign in to access the application. <br />When **No** is selected, anonymous users are not allowed. End-users have to sign in to access the application. |
 | Anonymous user role   | The user role that end-users of your application have when they are not signed in. This tells the application which role should be automatically applied to anonymous users who access the app. The **Allow anonymous users** property should be set to **Yes** to select an anonymous user role. |
 
+{{% alert color="warning" %}}
+Enabling anonymous users allows anyone to start using your app without signing in. If you do not secure your data with appropriate entity access rules for the anonymous user role, this can lead to unintended data exposure.
+{{% /alert %}}
+
 ## Read More
 
 * [App Security](/refguide/app-security/)