feat: add missing SOCKS5 features

Goal of this commit is to add some missing features when the
Kubernetes API is accessed through a SOCKS5 proxy. That's for
example the case when port-forwarding is used (`kubectl port-forward`)
or when exec'ing inside a container (`kubectl exec`), with this
commit it'll now be possible to use both.

Signed-off-by: Romain Aviolat <romain.aviolat@kudelskisecurity.com>
Signed-off-by: Romain Jufer <romain.jufer@kudelskisecurity.com>

vendor/github.com/armon/go-socks5/ruleset.go

@@ -0,0 +1,41 @@
+package socks5
+
+import (
+	"golang.org/x/net/context"
+)
+
+// RuleSet is used to provide custom rules to allow or prohibit actions
+type RuleSet interface {
+	Allow(ctx context.Context, req *Request) (context.Context, bool)
+}
+
+// PermitAll returns a RuleSet which allows all types of connections
+func PermitAll() RuleSet {
+	return &PermitCommand{true, true, true}
+}
+
+// PermitNone returns a RuleSet which disallows all types of connections
+func PermitNone() RuleSet {
+	return &PermitCommand{false, false, false}
+}
+
+// PermitCommand is an implementation of the RuleSet which
+// enables filtering supported commands
+type PermitCommand struct {
+	EnableConnect   bool
+	EnableBind      bool
+	EnableAssociate bool
+}
+
+func (p *PermitCommand) Allow(ctx context.Context, req *Request) (context.Context, bool) {
+	switch req.Command {
+	case ConnectCommand:
+		return ctx, p.EnableConnect
+	case BindCommand:
+		return ctx, p.EnableBind
+	case AssociateCommand:
+		return ctx, p.EnableAssociate
+	}
+
+	return ctx, false
+}