I use CasperJS - it's a wrapper with syntactic sugar around PhantomJS. Posting to social networks is almost trivial (couple of lines). Just run it with your cookies file, and it'll login automatically.
I've found bing login for casperjs, but otherwise most example out there assume anonymous access. I wouldn't use my cookie files, especially because it limits automation.
It is so stunning that nobody tried to solve this before / nobody published the scripts.