Technical Tip: Allowing website access from blocklists with backend and frontend URLs

When accessing a website, the URL entered in the browser (for example, https://fortinet.com) typically represents only the frontend application. 
However, some sites may rely on additional backend domains to deliver resources such as data, images, scripts, authentication, or updates. Therefore, if a FortiGate web filter is configured to recognize the visible frontend domain, it may also block these backend calls. This will result in the site being partially or completely unusable.

For example, a legitimate site like (https://pkf.greythrpro.com/login) appears blocked by a category-based web filter.
Exempting only the visible URL won’t work, because the filtering is triggered by the backend domain the site uses — in this case (https://prod.greythrpro.com/ ), as shown in the FortiGate denied traffic logs (see attachment below).

Thus, to ensure successful access to this website, administrators should whitelist the related backend/CDN domains or both the frontend URLs for the best results (see attachment below).

Related articles:
Technical Tip: Using a static URL filter feature to allow/block web sites
Technical Tip: Whitelist IP addresses and URLs using firewall policies