The problem was an ActionFilter in ControllerBase class. (i didn't see it the first time)
It was like
[ActionFilters.RequireHttps(RequireSecure = false)]
Had to set it on 'true'
Thank you all for your answers.
Note:
Represents the base class for all action-filter attributes
Namespace: System.Web.Http.Filters
Assembly: System.Web.Http (in System.Web.Http.dll)