Support tailscale configuration via Caddy configuration

Caddyfile

@@ -1,5 +1,12 @@
 {
 	order tailscale_auth after basicauth
+	tailscale {
+		auth_key "tskey-auth-"
+
+		caddy {
+			auth_key "tskey-auth-caddy"
+		}
+	}
 }
 
 :80 {

app.go

@@ -0,0 +1,45 @@
+package tscaddy
+
+import (
+	"github.com/caddyserver/caddy/v2"
+)
+
+func init() {
+	caddy.RegisterModule(TSApp{})
+}
+
+type TSApp struct {
+	// DefaultAuthKey is the default auth key to use for Tailscale if no other auth key is specified.
+	DefaultAuthKey string `json:"auth_key,omitempty" caddy:"namespace=tailscale.auth_key"`
+
+	Ephemeral bool `json:"ephemeral,omitempty" caddy:"namespace=tailscale.ephemeral"`
+
+	Servers map[string]TSServer `json:"servers,omitempty" caddy:"namespace=tailscale"`
+}
+
+type TSServer struct {
+	AuthKey string `json:"auth_key,omitempty" caddy:"namespace=auth_key"`
+
+	Ephemeral bool `json:"ephemeral,omitempty" caddy:"namespace=tailscale.ephemeral"`
+
+	name string
+}
+
+func (TSApp) CaddyModule() caddy.ModuleInfo {
+	return caddy.ModuleInfo{
+		ID:  "tailscale",
+		New: func() caddy.Module { return new(TSApp) },
+	}
+}
+
+func (t *TSApp) Start() error {
+	tsapp.Store(t)
+	return nil
+}
+
+func (t *TSApp) Stop() error {
+	tsapp.CompareAndSwap(t, nil)
+	return nil
+}
+
+var _ caddy.App = (*TSApp)(nil)

caddyfile.go

@@ -0,0 +1,77 @@
+package tscaddy
+
+import (
+	"github.com/caddyserver/caddy/v2/caddyconfig"
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+)
+
+func init() {
+	httpcaddyfile.RegisterGlobalOption("tailscale", parseApp)
+}
+
+func parseApp(d *caddyfile.Dispenser, _ any) (any, error) {
+	app := &TSApp{
+		Servers: make(map[string]TSServer),
+	}
+	if !d.Next() {
+		return app, d.ArgErr()
+
+	}
+
+	for d.NextBlock(0) {
+		val := d.Val()
+
+		switch val {
+		case "auth_key":
+			if !d.NextArg() {
+				return nil, d.ArgErr()
+			}
+			app.DefaultAuthKey = d.Val()
+		case "ephemeral":
+			app.Ephemeral = true
+		default:
+			svr, err := parseServer(d)
+			if app.Servers == nil {
+				app.Servers = map[string]TSServer{}
+			}
+			if err != nil {
+				return nil, err
+			}
+			app.Servers[svr.name] = svr
+		}
+	}
+
+	return httpcaddyfile.App{
+		Name:  "tailscale",
+		Value: caddyconfig.JSON(app, nil),
+	}, nil
+}
+
+func parseServer(d *caddyfile.Dispenser) (TSServer, error) {
+	name := d.Val()
+	segment := d.NewFromNextSegment()
+
+	if !segment.Next() {
+		return TSServer{}, d.ArgErr()
+	}
+
+	svr := TSServer{}
+	svr.name = name
+	for nesting := segment.Nesting(); segment.NextBlock(nesting); {
+		val := segment.Val()
+		switch val {
+		case "auth_key":
+			if !segment.NextArg() {
+				return svr, segment.ArgErr()
+			}
+			svr.AuthKey = segment.Val()
+		case "ephemeral":
+			svr.Ephemeral = true
+		default:
+			return svr, segment.Errf("unrecognized subdirective: %s", segment.Val())
+		}
+	}
+
+	return svr, nil
+}

caddyfile_test.go

@@ -0,0 +1,114 @@
+package tscaddy
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
+	"github.com/caddyserver/caddy/v2/caddyconfig/httpcaddyfile"
+	"github.com/google/go-cmp/cmp"
+)
+
+func Test_ParseApp(t *testing.T) {
+	tests := []struct {
+		name    string
+		d       *caddyfile.Dispenser
+		want    string
+		authKey string
+		wantErr bool
+	}{
+		{
+
+			name: "empty",
+			d: caddyfile.NewTestDispenser(`
+				tailscsale {}
+			`),
+			want: `{}`,
+		},
+		{
+			name: "auth_key",
+			d: caddyfile.NewTestDispenser(`
+				tailscsale {
+					auth_key abcdefghijklmnopqrstuvwxyz
+				}`),
+			want:    `{"auth_key":"abcdefghijklmnopqrstuvwxyz"}`,
+			authKey: "abcdefghijklmnopqrstuvwxyz",
+		},
+		{
+			name: "ephemeral",
+			d: caddyfile.NewTestDispenser(`
+				tailscsale {
+					ephemeral
+				}`),
+			want:    `{"ephemeral":true}`,
+			authKey: "",
+		},
+		{
+			name: "missing auth key",
+			d: caddyfile.NewTestDispenser(`
+				tailscsale {
+					auth_key
+				}`),
+			wantErr: true,
+		},
+		{
+			name: "empty server",
+			d: caddyfile.NewTestDispenser(`
+				tailscsale {
+					foo
+				}`),
+			want: `{"servers":{"foo":{}}}`,
+		},
+		{
+			name: "tailscale with server",
+			d: caddyfile.NewTestDispenser(`
+				tailscsale {
+					auth_key 1234567890
+					foo {
+						auth_key  abcdefghijklmnopqrstuvwxyz
+					}
+				}`),
+			want:    `{"auth_key":"1234567890","servers":{"foo":{"auth_key":"abcdefghijklmnopqrstuvwxyz"}}}`,
+			wantErr: false,
+			authKey: "abcdefghijklmnopqrstuvwxyz",
+		},
+	}
+
+	for _, testcase := range tests {
+		t.Run(testcase.name, func(t *testing.T) {
+			got, err := parseApp(testcase.d, nil)
+			if err != nil {
+				if !testcase.wantErr {
+					t.Errorf("parseApp() error = %v, wantErr %v", err, testcase.wantErr)
+					return
+				}
+				return
+			}
+			if testcase.wantErr && err == nil {
+				t.Errorf("parseApp() err = %v, wantErr %v", err, testcase.wantErr)
+				return
+			}
+			gotJSON := string(got.(httpcaddyfile.App).Value)
+			if diff := compareJSON(gotJSON, testcase.want, t); diff != "" {
+				t.Errorf("parseApp() diff(-got +want):\n%s", diff)
+			}
+			app := new(TSApp)
+			if err := json.Unmarshal([]byte(gotJSON), &app); err != nil {
+				t.Error("failed to unmarshal json into TSApp")
+			}
+		})
+	}
+
+}
+
+func compareJSON(s1, s2 string, t *testing.T) string {
+	var v1, v2 map[string]any
+	if err := json.Unmarshal([]byte(s1), &v1); err != nil {
+		t.Error(err)
+	}
+	if err := json.Unmarshal([]byte(s2), &v2); err != nil {
+		t.Error(err)
+	}
+
+	return cmp.Diff(v1, v2)
+}

go.mod

@@ -4,6 +4,7 @@ go 1.22.0
 
 require (
 	github.com/caddyserver/caddy/v2 v2.7.3
+	github.com/google/go-cmp v0.6.0
 	go.uber.org/zap v1.26.0
 	tailscale.com v1.62.0
 )
@@ -62,7 +63,6 @@ require (
 	github.com/golang/snappy v0.0.4 // indirect
 	github.com/google/btree v1.1.2 // indirect
 	github.com/google/cel-go v0.15.1 // indirect
-	github.com/google/go-cmp v0.6.0 // indirect
 	github.com/google/nftables v0.1.1-0.20230115205135-9aa6fdf5a28c // indirect
 	github.com/google/pprof v0.0.0-20230808223545-4887780b67fb // indirect
 	github.com/google/uuid v1.5.0 // indirect

module.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"sync/atomic"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
@@ -22,6 +23,7 @@ import (
 
 var (
 	servers = caddy.NewUsagePool()
+	tsapp   = atomic.Pointer[TSApp]{}
 )
 
 func init() {
@@ -47,7 +49,10 @@ func getPlainListener(_ context.Context, _ string, addr string, _ net.ListenConf
 		network = "tcp"
 	}
 
-	return s.Listen(network, ":"+port)
+	ln := &tsnetServerDestructor{
+		Server: s.Server,
+	}
+	return ln.Listen(network, ":"+port)
 }
 
 func getTLSListener(_ context.Context, _ string, addr string, _ net.ListenConfig) (any, error) {
@@ -105,11 +110,9 @@ func getServer(_, addr string) (*tsnetServerDestructor, error) {
 		}
 
 		if host != "" {
-			// Set authkey to "TS_AUTHKEY_<HOST>".  If empty,
-			// fall back to "TS_AUTHKEY".
-			s.AuthKey = os.Getenv("TS_AUTHKEY_" + strings.ToUpper(host))
-			if s.AuthKey == "" {
-				s.AuthKey = os.Getenv("TS_AUTHKEY")
+			if app := tsapp.Load(); app != nil {
+				s.AuthKey = getAuthKey(host, app)
+				s.Ephemeral = getEphemeral(host, app)
 			}
 
 			// Set config directory for tsnet.  By default, tsnet will use the name of the
@@ -136,6 +139,39 @@ func getServer(_, addr string) (*tsnetServerDestructor, error) {
 	return s.(*tsnetServerDestructor), nil
 }
 
+func getAuthKey(host string, app *TSApp) string {
+	if app == nil {
+		return ""
+	}
+	svr := app.Servers[host]
+	if svr.AuthKey != "" {
+		return svr.AuthKey
+	}
+
+	if app.DefaultAuthKey != "" {
+		return app.DefaultAuthKey
+	}
+
+	// Set authkey to "TS_AUTHKEY_<HOST>".  If empty,
+	// fall back to "TS_AUTHKEY".
+	authKey := os.Getenv("TS_AUTHKEY_" + strings.ToUpper(host))
+	if authKey == "" {
+		authKey = os.Getenv("TS_AUTHKEY")
+	}
+	return authKey
+}
+
+func getEphemeral(host string, app *TSApp) bool {
+	if app == nil {
+		return false
+	}
+	if svr, ok := app.Servers[host]; ok {
+		return svr.Ephemeral
+	}
+
+	return app.Ephemeral
+}
+
 type TailscaleAuth struct {
 	localclient *tailscale.LocalClient
 }
@@ -234,3 +270,31 @@ type tsnetServerDestructor struct {
 func (t tsnetServerDestructor) Destruct() error {
 	return t.Close()
 }
+
+func (t *tsnetServerDestructor) Listen(network string, addr string) (net.Listener, error) {
+	ln, err := t.Server.Listen(network, addr)
+	if err != nil {
+		return nil, err
+	}
+	serverListener := &tsnetServerListener{
+		hostname: t.Hostname,
+		Listener: ln,
+	}
+	return serverListener, nil
+}
+
+type tsnetServerListener struct {
+	hostname string
+	net.Listener
+}
+
+func (t *tsnetServerListener) Close() error {
+	if err := t.Listener.Close(); err != nil {
+		return err
+	}
+
+	// Decrement usage count of server for this hostname.
+	// If usage reaches zero, then the server is actually shutdown.
+	_, err := servers.Delete(t.hostname)
+	return err
+}