Generate "Authorization: Basic authString"
in a HTTP request header to be forwarded to a server,
if it does not have an original Authorization field from a client.
The authString should be "userName:passWord".
The following special string stand for attributes of clients.
-- user name got using Ident protocol
-- host name of the client got from the socket
-- host name of the network interface to the client
-- like %i but use the value of "Host:" if given in HTTP