Hi,
The problem is caused by a bug when you have a password on the certificate you are importing. Unreal creates a hidden window to do the importing and it’s the hidden window that is asking for your password. That is fixed in 4.17, and you can find the fix here if you’re using Github.
For the certificates you import on the Mac, you need to import them into the System keychain and also allow access to all programs.
We have improved the remote toolchain signing process for 4.18 and there will no longer be any need to configure anything on the Mac.
Cheers
Jack