I log into Stack Overflow (and others) using Google. I don't have any alternative means of login in many cases, like an email/password combination - Google is the only way of accessing those accounts.
Now the scenario is that I am on an untrusted computer and want to access eg. Stack Overflow. However, I don't want to log in to Google as I would put my primary email at risk.
How can I log in to SO/some other service anyway?