caddytls: Support external certificate Managers (like Tailscale) (#4541)

Huge thank-you to Tailscale (https://tailscale.com) for making this change possible!
This is a great feature for Caddy and Tailscale is a great fit for a standard implementation.

* caddytls: GetCertificate modules; Tailscale

* Caddyfile support for get_certificate

Also fix AP provisioning in case of empty subject list (persist loaded
module on struct, much like Issuers, to surive reprovisioning).

And implement start of HTTP cert getter, still WIP.

* Update modules/caddytls/automation.go

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

* Use tsclient package, check status for name

* Implement HTTP cert getter

And use reuse CertMagic's PEM functions for private keys.

* Remove cache option from Tailscale getter

Tailscale does its own caching and we don't need the added complexity...
for now, at least.

* Several updates

- Option to disable cert automation in auto HTTPS
- Support multiple cert managers
- Remove cache feature from cert manager modules
- Minor improvements to auto HTTPS logging

* Run go mod tidy

* Try to get certificates from Tailscale implicitly

Only for domains ending in .ts.net.

I think this is really cool!

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

4 files changed, 39 insertions, 7 deletions

diff --git a/caddyconfig/httpcaddyfile/builtins.go b/caddyconfig/httpcaddyfile/builtins.go
index 7fdd3e8..2606bf3 100644
--- a/caddyconfig/httpcaddyfile/builtins.go
+++ b/caddyconfig/httpcaddyfile/builtins.go
@@ -82,6 +82,7 @@ func parseBind(h Helper) ([]ConfigValue, error) {
 //         on_demand
 //         eab    <key_id> <mac_key>
 //         issuer <module_name> [...]
+//         get_certificate <module_name> [...]
 //     }
 //
 func parseTLS(h Helper) ([]ConfigValue, error) {
@@ -93,6 +94,7 @@ func parseTLS(h Helper) ([]ConfigValue, error) {
 	var keyType string
 	var internalIssuer *caddytls.InternalIssuer
 	var issuers []certmagic.Issuer
+	var certManagers []certmagic.CertificateManager
 	var onDemand bool
 
 	for h.Next() {
@@ -307,6 +309,22 @@ func parseTLS(h Helper) ([]ConfigValue, error) {
 				}
 				issuers = append(issuers, issuer)
 
+			case "get_certificate":
+				if !h.NextArg() {
+					return nil, h.ArgErr()
+				}
+				modName := h.Val()
+				modID := "tls.get_certificate." + modName
+				unm, err := caddyfile.UnmarshalModule(h.Dispenser, modID)
+				if err != nil {
+					return nil, err
+				}
+				certManager, ok := unm.(certmagic.CertificateManager)
+				if !ok {
+					return nil, h.Errf("module %s (%T) is not a certmagic.CertificateManager", modID, unm)
+				}
+				certManagers = append(certManagers, certManager)
+
 			case "dns":
 				if !h.NextArg() {
 					return nil, h.ArgErr()
@@ -453,6 +471,12 @@ func parseTLS(h Helper) ([]ConfigValue, error) {
 			Value: true,
 		})
 	}
+	for _, certManager := range certManagers {
+		configVals = append(configVals, ConfigValue{
+			Class: "tls.cert_manager",
+			Value: certManager,
+		})
+	}
 
 	// custom certificate selection
 	if len(certSelector.AnyTag) > 0 {
diff --git a/caddyconfig/httpcaddyfile/httptype.go b/caddyconfig/httpcaddyfile/httptype.go
index 3a54c08..d7716a4 100644
--- a/caddyconfig/httpcaddyfile/httptype.go
+++ b/caddyconfig/httpcaddyfile/httptype.go
@@ -446,13 +446,14 @@ func (st *ServerType) serversFromPairings(
 		// handle the auto_https global option
 		if autoHTTPS != "on" {
 			srv.AutoHTTPS = new(caddyhttp.AutoHTTPSConfig)
-			if autoHTTPS == "off" {
+			switch autoHTTPS {
+			case "off":
 				srv.AutoHTTPS.Disabled = true
-			}
-			if autoHTTPS == "disable_redirects" {
+			case "disable_redirects":
 				srv.AutoHTTPS.DisableRedir = true
-			}
-			if autoHTTPS == "ignore_loaded_certs" {
+			case "disable_certs":
+				srv.AutoHTTPS.DisableCerts = true
+			case "ignore_loaded_certs":
 				srv.AutoHTTPS.IgnoreLoadedCerts = true
 			}
 		}
diff --git a/caddyconfig/httpcaddyfile/options.go b/caddyconfig/httpcaddyfile/options.go
index 016d0df..65b0338 100644
--- a/caddyconfig/httpcaddyfile/options.go
+++ b/caddyconfig/httpcaddyfile/options.go
@@ -384,8 +384,8 @@ func parseOptAutoHTTPS(d *caddyfile.Dispenser, _ interface{}) (interface{}, erro
 	if d.Next() {
 		return "", d.ArgErr()
 	}
-	if val != "off" && val != "disable_redirects" && val != "ignore_loaded_certs" {
-		return "", d.Errf("auto_https must be one of 'off', 'disable_redirects' or 'ignore_loaded_certs'")
+	if val != "off" && val != "disable_redirects" && val != "disable_certs" && val != "ignore_loaded_certs" {
+		return "", d.Errf("auto_https must be one of 'off', 'disable_redirects', 'disable_certs', or 'ignore_loaded_certs'")
 	}
 	return val, nil
 }
diff --git a/caddyconfig/httpcaddyfile/tlsapp.go b/caddyconfig/httpcaddyfile/tlsapp.go
index b11addc..48506d8 100644
--- a/caddyconfig/httpcaddyfile/tlsapp.go
+++ b/caddyconfig/httpcaddyfile/tlsapp.go
@@ -133,6 +133,13 @@ func (st ServerType) buildTLSApp(
 				ap.Issuers = issuers
 			}
 
+			// certificate managers
+			if certManagerVals, ok := sblock.pile["tls.cert_manager"]; ok {
+				for _, certManager := range certManagerVals {
+					certGetterName := certManager.Value.(caddy.Module).CaddyModule().ID.Name()
+					ap.ManagersRaw = append(ap.ManagersRaw, caddyconfig.JSONModuleObject(certManager.Value, "via", certGetterName, &warnings))
+				}
+			}
 			// custom bind host
 			for _, cfgVal := range sblock.pile["bind"] {
 				for _, iss := range ap.Issuers {