Apple - How do I trust a self-signed certificate in iOS 10.3?

I've identified that the specific parameter that Apple looks for when allowing you to manually trust a certificate is the CA Basic Constraint (E.G. critical,CA:true). If the certificate has this extension, the system will allow you to manually trust the certificate.

However the process has one extra step (as opposed to iOS 9.3):

1. Export the certificate as PEM format
2. Send the certificate to the device (Safari, Email, AirDrop, etc...) and open it
3. A message will appear telling you the profile has been downloaded.
4. Open the settings app and tap the "Profile Downloaded" item below your Apple ID row.
5. Install the Certificate. You will have to provide your devices passcode.
6. Navigate to Settings -> General -> About -> Certificate Trust Settings
7. Enable full trust for your certificate