如何在Django 1.9中使用自定义继承用户作为身份验证?

I'm somewhat new in Django, and I'm trying to extract user info from a form, the problem arises when I try to save that form info into the database, as the user info it gets is from default Users model, but the model being saved ("Mensaje") has a Foreign Key relationship with the extended User model I use (called "Usuario"), so the engine fails when I try to put the form info into the model.I'm somewhat new in Django, and I'm trying to e