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/sys_asmreqn.go

@@ -0,0 +1,42 @@
+// 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 freebsd linux
+
+package ipv4
+
+import (
+	"net"
+	"unsafe"
+
+	"golang.org/x/net/internal/socket"
+)
+
+func (so *sockOpt) getIPMreqn(c *socket.Conn) (*net.Interface, error) {
+	b := make([]byte, so.Len)
+	if _, err := so.Get(c, b); err != nil {
+		return nil, err
+	}
+	mreqn := (*ipMreqn)(unsafe.Pointer(&b[0]))
+	if mreqn.Ifindex == 0 {
+		return nil, nil
+	}
+	ifi, err := net.InterfaceByIndex(int(mreqn.Ifindex))
+	if err != nil {
+		return nil, err
+	}
+	return ifi, nil
+}
+
+func (so *sockOpt) setIPMreqn(c *socket.Conn, ifi *net.Interface, grp net.IP) error {
+	var mreqn ipMreqn
+	if ifi != nil {
+		mreqn.Ifindex = int32(ifi.Index)
+	}
+	if grp != nil {
+		mreqn.Multiaddr = [4]byte{grp[0], grp[1], grp[2], grp[3]}
+	}
+	b := (*[sizeofIPMreqn]byte)(unsafe.Pointer(&mreqn))[:sizeofIPMreqn]
+	return so.Set(c, b)
+}