How to disable auto password filling (Keychain) while in private browsing mode in Safari?

Keychain offers to auto complete forms including passwords even in private browsing mode. How can I disable this?

I'm using Safari 8.0.5 on Yosemite 10.10.3.

Edit: The use case here is when other people need to borrow my computer. I'll open a private browsing window for them. I don't want my credentials auto-filling when they visit site.

Solution 1:

There is no way currently offered by Apple to disable auto-fill based on the browsing mode. However, you could try to switch auto-fill on/off based browsing mode by making a trigger-effect script or macro with AppleScript or an application like Keyboard Maestro.

Solution 2:

Not sure why do you need it, but my guess is to allow others to use safari without leaving traces of their activity. Private mode is not what you need. Private mode is useful when you need to access a website without tracking cookies and history and only then.

What you probably need is enabling the Guest account in user accounts. Let others login as a Guest and everything they did, including internet, will be removed upon the logout.