If you wish to whitelist a specific User-Agent you believe to be legit, please follow this workaround :
1. Click "User Defined Request rules" under the category "Bad User Agents Signatures \ Fake Browsers".
2. Click Add New Rule. The New Rule wizard appears.
3. Choose "Search in User-Agent header"
4. In the Create pattern window, in the Pattern to Search field, enter the user agent string you wish to allow.
5. Select "Allow request" / "Block request"
6. Choose whether you want this rule to apply to all pages or specific pages.
Best of luck,
We are here in case you have further questions.