loginUDG read credentials from file

[jesusff]

Hi,

In order to avoid showing my UDG user/password openly in notebooks/scripts I usually do:

do.call(loginUDG, as.list(readLines("udg_login.txt")))

which is quite dirty for the purpose. I think this could be easily implemented internally in loginUDG(), either as e.g.:

loginUDG(from.file = "udg_login.txt")

Or just let the function try to find a default file (e.g. ~/.udgrc) when called without arguments loginUDG()

[cofinoa]

we need to create a .rc simmilar to the netcdf-c support on authentication:
https://docs.unidata.ucar.edu/netcdf-c/current/tutorial_8dox.html

more over the section on third-party auth, based also on .netrc "standard"