I've been using Last Pass, its a free app, but because you can't get plugins into Metro IE it won't automatically enter credentials. It has a work around of using copy and paste and also comes with it's own browser which does automate entering credentials for you, but the browser usability is not great.
Actually, there is a way to get LastPass fill-ins to work. Basically 1) go to Desktop and open IE. 2) Open the Favorites panel. 3) Go to LP site and log in. 4) Find their bookmarklets and drag the ones you want (such as Fill In) to your IE Favorites. After that you can use the bookmarklets via the regular Surface RT IE browser. If you need more details, there is a blog post on this somewhere, just search for "surface lastpass"
So I'm able to get logins out of Lastpass. My challenge is getting data INTO lastpass! I'm on day 2 of my trial after years of using RoboForm. RoboForm recognized when I was entering a password into a new site (like this forum) and would automatically ask me if I wanted to save the password. Super easy. It seems with LP I have to be using their browser or the Surface Desktop IE browser. And even then I have to remember to tell LP I want to save the data, before I click submit. It's a lot of extra steps compared to RF. But RF doesn't seem to have much interest in Windows Phone or Surface, and their interface is very dated anyway.
So frustrating trying to find a good password collector & login tool!