Depending on the use case and usage patterns which I'm not sure we have the information to know, I'm just curious if it might be easier to whitelist safe domain

Depending on the use case and usage patterns which I'm not sure we have the information to know, I'm just curious if it might be easier to whitelist safe domains rather than to try and blacklist dangerous domains? No blacklist is ever going to be comprehensive, and the possibility for false positives with a blacklist is pretty substantial. But you can cover a pretty substantial part of typical peoples web browsing just by selecting say the top 1,000 US domains and figuring out which ones are generally safe enough to have a green light with your App. This might not work with your app's use case, however, especially if generally obscure URLs are used with your site.