C: On the Static URL Filter configuration, set Action to Exempt.
Based on the exhibit, the administrator has configured the FortiGuard Category Based Filter to block access to all social networking sites, and has also configured a Static URL Filter to block access to twitter.com. As a result, users are being redirected to a block page when they try to access twitter.com.
To allow users to access twitter.com while blocking all other social networking sites, the administrator can make the following configuration change:
On the Static URL Filter configuration, set Action to Exempt: By setting the Action to Exempt, the administrator can override the block on twitter.com that was specified in the FortiGuard Category Based Filter. This will allow users to access twitter.com, while all other social networking sites will still be blocked.
Note:
Tested this in a lab environment and to make this work as stated in the question the Exempt action is the only way to go, and also *.twimg.com will has to be added to the URL Filter with an Exempt action for this situation to really work!
Allow: Access is permitted. Traffic is passed to remaining operations, including FortiGuard web filter, web content filter, web script filters, and antivirus scanning.
Exempt: Allows traffic from trusted sources to bypass all security inspections.