Bing Webmaster Tools now lets you log in using your Google account, Facebook account or your Microsoft login. This is to help make it easier for webmasters to log into their toolset.
Here is what the interface looks like now when you try to log in:
Microsoft told us this “means that the messages Webmaster Tools may occasionally send you about your managed properties will be sent to the email account associated with the webmaster tools account you are logged in with. The most recent messages will still be available in your Webmaster Tools Message Center.”
This should be available as a login option for all users who verified their websites with Bing Webmaster Tools at bing.com/toolbox/webmaster.