One ideal might be to flag the connection has requiring credentials so that when the user tries to connect with it we can know to prompt for credentials, but credentials are more than just a password, so a modal that prompts just for credentials could be really tricky to pull off.

The simplest, most versatile fix might be if we just have a setting that disables storing connections. Then the only buttons on the connection form would be Connect and Cancel. So no Save, no Save & Connect. And the connection just doesn't get saved. We have the concept of a connection that doesn't get saved for the autoconnect connections already. That wouldn't require much design and it sidesteps the problem mentioned above.

This would probably be 3 points. A modal that prompts for credentials would likely be much more. Alternatively we could know to pop up the usual edit modal in that case, but that's a bit maybe a bit hacky?