When using a loadable module in Zabbix, is not allowed to use the fields Username and Password that loads in screen of item configuration when is select the type "simple check". These values are not passed to module when calling it. These fields only was passed when using vmfunc function.
The problem is the code on checks_simple.c that only call the module by function process():
My solution was to duplicate the function process with name process_simple (because it used by other things) and call it unless of call process, but passing Username and Password (patch attached).
I think that passing username and password using the default fields for this in simple check - not in parameters of function - is the "elegant" way of to do this.