Use caddy's certmagic library for extensible/robust ACME handling (#14177)

* use certmagic for more extensible/robust ACME cert handling

* accept TOS based on config option

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/golang.org/x/net/ipv4/control_pktinfo.go

@@ -0,0 +1,39 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin linux solaris
+
+package ipv4
+
+import (
+	"net"
+	"unsafe"
+
+	"golang.org/x/net/internal/iana"
+	"golang.org/x/net/internal/socket"
+)
+
+func marshalPacketInfo(b []byte, cm *ControlMessage) []byte {
+	m := socket.ControlMessage(b)
+	m.MarshalHeader(iana.ProtocolIP, sysIP_PKTINFO, sizeofInetPktinfo)
+	if cm != nil {
+		pi := (*inetPktinfo)(unsafe.Pointer(&m.Data(sizeofInetPktinfo)[0]))
+		if ip := cm.Src.To4(); ip != nil {
+			copy(pi.Spec_dst[:], ip)
+		}
+		if cm.IfIndex > 0 {
+			pi.setIfindex(cm.IfIndex)
+		}
+	}
+	return m.Next(sizeofInetPktinfo)
+}
+
+func parsePacketInfo(cm *ControlMessage, b []byte) {
+	pi := (*inetPktinfo)(unsafe.Pointer(&b[0]))
+	cm.IfIndex = int(pi.Ifindex)
+	if len(cm.Dst) < net.IPv4len {
+		cm.Dst = make(net.IP, net.IPv4len)
+	}
+	copy(cm.Dst, pi.Addr[:])
+}