my question seems to be dumb, but because am making an application that all the pages needs to get the users authentification, and because am using HTML5 so,
It depends on exactly what you are trying to do, but the question Microformats solve is "How can I make this HTML easily understandably by a computer?".
If you think that a computer will ever need to parse out the data in a meaningful way, then use it.
This could be either Google (though in your case, it won't be able to log in), an internal search you write at some point, a browser extension to highlight some sort of information etc.
In short though, it's unlikely to be useful, but on the other hand it's not hard to implement!