func SOCKS5(network, address string, auth *Auth, forward Dialer) (Dialer, error) {
	d := socks.NewDialer(network, address)
	if forward != nil {
		if f, ok := forward.(ContextDialer); ok {
			d.ProxyDial = func(ctx context.Context, network string, address string) (net.Conn, error) {
				return f.DialContext(ctx, network, address)
			}
		} else {
			d.ProxyDial = func(ctx context.Context, network string, address string) (net.Conn, error) {
				return dialContext(ctx, forward, network, address)
			}
		}
	}
	if auth != nil {
		up := socks.UsernamePassword{
			Username: auth.User,
			Password: auth.Password,
		}
		d.AuthMethods = []socks.AuthMethod{
			socks.AuthMethodNotRequired,
			socks.AuthMethodUsernamePassword,
		}
		d.Authenticate = up.Authenticate
	}
	return d, nil
}
SOCKS5 returns a Dialer that makes SOCKSv5 connections to the given
address with an optional username and password.
See RFC 1928 and RFC 1929.
package proxy
import (
	"context"
	"net"
	"golang.org/x/net/internal/socks"
)