[R] Proxy config in R for windows

[Kenneth Roy Cabrera Torres]

Hi R users:

I know that the --internet2 options enable me in Windows to download 
packages in R,
but now, in my university the put a usename and password configuration 
for the proxy.

How can I configure R to take the proxy password and username.

I linux I solve the problem when I configre the
export http_proxy="username:pass at server:port"

But I don´t know how to make it in windows.

Kenneth