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/github.com/miekg/dns/clientconfig.go

@@ -0,0 +1,135 @@
+package dns
+
+import (
+	"bufio"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// ClientConfig wraps the contents of the /etc/resolv.conf file.
+type ClientConfig struct {
+	Servers  []string // servers to use
+	Search   []string // suffixes to append to local name
+	Port     string   // what port to use
+	Ndots    int      // number of dots in name to trigger absolute lookup
+	Timeout  int      // seconds before giving up on packet
+	Attempts int      // lost packets before giving up on server, not used in the package dns
+}
+
+// ClientConfigFromFile parses a resolv.conf(5) like file and returns
+// a *ClientConfig.
+func ClientConfigFromFile(resolvconf string) (*ClientConfig, error) {
+	file, err := os.Open(resolvconf)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+	return ClientConfigFromReader(file)
+}
+
+// ClientConfigFromReader works like ClientConfigFromFile but takes an io.Reader as argument
+func ClientConfigFromReader(resolvconf io.Reader) (*ClientConfig, error) {
+	c := new(ClientConfig)
+	scanner := bufio.NewScanner(resolvconf)
+	c.Servers = make([]string, 0)
+	c.Search = make([]string, 0)
+	c.Port = "53"
+	c.Ndots = 1
+	c.Timeout = 5
+	c.Attempts = 2
+
+	for scanner.Scan() {
+		if err := scanner.Err(); err != nil {
+			return nil, err
+		}
+		line := scanner.Text()
+		f := strings.Fields(line)
+		if len(f) < 1 {
+			continue
+		}
+		switch f[0] {
+		case "nameserver": // add one name server
+			if len(f) > 1 {
+				// One more check: make sure server name is
+				// just an IP address.  Otherwise we need DNS
+				// to look it up.
+				name := f[1]
+				c.Servers = append(c.Servers, name)
+			}
+
+		case "domain": // set search path to just this domain
+			if len(f) > 1 {
+				c.Search = make([]string, 1)
+				c.Search[0] = f[1]
+			} else {
+				c.Search = make([]string, 0)
+			}
+
+		case "search": // set search path to given servers
+			c.Search = append([]string(nil), f[1:]...)
+
+		case "options": // magic options
+			for _, s := range f[1:] {
+				switch {
+				case len(s) >= 6 && s[:6] == "ndots:":
+					n, _ := strconv.Atoi(s[6:])
+					if n < 0 {
+						n = 0
+					} else if n > 15 {
+						n = 15
+					}
+					c.Ndots = n
+				case len(s) >= 8 && s[:8] == "timeout:":
+					n, _ := strconv.Atoi(s[8:])
+					if n < 1 {
+						n = 1
+					}
+					c.Timeout = n
+				case len(s) >= 9 && s[:9] == "attempts:":
+					n, _ := strconv.Atoi(s[9:])
+					if n < 1 {
+						n = 1
+					}
+					c.Attempts = n
+				case s == "rotate":
+					/* not imp */
+				}
+			}
+		}
+	}
+	return c, nil
+}
+
+// NameList returns all of the names that should be queried based on the
+// config. It is based off of go's net/dns name building, but it does not
+// check the length of the resulting names.
+func (c *ClientConfig) NameList(name string) []string {
+	// if this domain is already fully qualified, no append needed.
+	if IsFqdn(name) {
+		return []string{name}
+	}
+
+	// Check to see if the name has more labels than Ndots. Do this before making
+	// the domain fully qualified.
+	hasNdots := CountLabel(name) > c.Ndots
+	// Make the domain fully qualified.
+	name = Fqdn(name)
+
+	// Make a list of names based off search.
+	names := []string{}
+
+	// If name has enough dots, try that first.
+	if hasNdots {
+		names = append(names, name)
+	}
+	for _, s := range c.Search {
+		names = append(names, Fqdn(name+s))
+	}
+	// If we didn't have enough dots, try after suffixes.
+	if !hasNdots {
+		names = append(names, name)
+	}
+	return names
+}