For what it's worth, the COD shows logon / login as completely interchangeable, (as it also does with 'logoff' and 'logout'); whatever, they should both have the same status.
As for 'intranet', I think this word is familiar to well-read native speakers of English in all parts of the English-speaking world (my personal definition of 'common'). Ergo, common should it be, imho.
MK