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/internal/socket/rawconn.go

@@ -0,0 +1,64 @@
+// Copyright 2017 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.
+
+package socket
+
+import (
+	"errors"
+	"net"
+	"os"
+	"syscall"
+)
+
+// A Conn represents a raw connection.
+type Conn struct {
+	network string
+	c       syscall.RawConn
+}
+
+// NewConn returns a new raw connection.
+func NewConn(c net.Conn) (*Conn, error) {
+	var err error
+	var cc Conn
+	switch c := c.(type) {
+	case *net.TCPConn:
+		cc.network = "tcp"
+		cc.c, err = c.SyscallConn()
+	case *net.UDPConn:
+		cc.network = "udp"
+		cc.c, err = c.SyscallConn()
+	case *net.IPConn:
+		cc.network = "ip"
+		cc.c, err = c.SyscallConn()
+	default:
+		return nil, errors.New("unknown connection type")
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &cc, nil
+}
+
+func (o *Option) get(c *Conn, b []byte) (int, error) {
+	var operr error
+	var n int
+	fn := func(s uintptr) {
+		n, operr = getsockopt(s, o.Level, o.Name, b)
+	}
+	if err := c.c.Control(fn); err != nil {
+		return 0, err
+	}
+	return n, os.NewSyscallError("getsockopt", operr)
+}
+
+func (o *Option) set(c *Conn, b []byte) error {
+	var operr error
+	fn := func(s uintptr) {
+		operr = setsockopt(s, o.Level, o.Name, b)
+	}
+	if err := c.c.Control(fn); err != nil {
+		return err
+	}
+	return os.NewSyscallError("setsockopt", operr)
+}