ipn/ipnlocal/serve: pass grant data in proxy header

Signed-off-by: Gesa Stupperich <gesa@tailscale.com>

cmd/tailscale/cli/serve_legacy.go

@@ -166,6 +166,7 @@ type serveEnv struct {
 	yes                 bool                // update without prompt
 	service             tailcfg.ServiceName // service name
 	tun                 bool                // redirect traffic to OS for service
+	forwardGrantHeaders string              // forward grants in headers
 
 	lc localServeClient // localClient interface, specific to serve
 

cmd/tailscale/cli/serve_v2.go

@@ -178,6 +178,7 @@ func newServeV2Command(e *serveEnv, subcmd serveMode) *ffcli.Command {
 			fs.UintVar(&e.https, "https", 0, "Expose an HTTPS server at the specified port (default mode)")
 			if subcmd == serve {
 				fs.UintVar(&e.http, "http", 0, "Expose an HTTP server at the specified port")
+				fs.StringVar(&e.forwardGrantHeaders, "forward-grant-headers", "", "Forward headers containing the values of the specified grants")
 			}
 			fs.UintVar(&e.tcp, "tcp", 0, "Expose a TCP forwarder to forward raw TCP packets at the specified port")
 			fs.UintVar(&e.tlsTerminatedTCP, "tls-terminated-tcp", 0, "Expose a TCP forwarder to forward TLS-terminated TCP packets at the specified port")
@@ -417,7 +418,7 @@ func (e *serveEnv) runServeCombined(subcmd serveMode) execFunc {
 			if len(args) > 0 {
 				target = args[0]
 			}
-			err = e.setServe(sc, dnsName, srvType, srvPort, mount, target, funnel, magicDNSSuffix)
+			err = e.setServe(sc, dnsName, srvType, srvPort, mount, target, funnel, magicDNSSuffix, e.forwardGrantHeaders)
 			msg = e.messageForPort(sc, st, dnsName, srvType, srvPort)
 		}
 		if err != nil {
@@ -611,12 +612,12 @@ func serveFromPortHandler(tcp *ipn.TCPPortHandler) serveType {
 	}
 }
 
-func (e *serveEnv) setServe(sc *ipn.ServeConfig, dnsName string, srvType serveType, srvPort uint16, mount string, target string, allowFunnel bool, mds string) error {
+func (e *serveEnv) setServe(sc *ipn.ServeConfig, dnsName string, srvType serveType, srvPort uint16, mount string, target string, allowFunnel bool, mds string, grantHeaders string) error {
 	// update serve config based on the type
 	switch srvType {
 	case serveTypeHTTPS, serveTypeHTTP:
 		useTLS := srvType == serveTypeHTTPS
-		err := e.applyWebServe(sc, dnsName, srvPort, useTLS, mount, target, mds)
+		err := e.applyWebServe(sc, dnsName, srvPort, useTLS, mount, target, mds, grantHeaders)
 		if err != nil {
 			return fmt.Errorf("failed apply web serve: %w", err)
 		}
@@ -780,7 +781,7 @@ func (e *serveEnv) messageForPort(sc *ipn.ServeConfig, st *ipnstate.Status, dnsN
 	return output.String()
 }
 
-func (e *serveEnv) applyWebServe(sc *ipn.ServeConfig, dnsName string, srvPort uint16, useTLS bool, mount, target string, mds string) error {
+func (e *serveEnv) applyWebServe(sc *ipn.ServeConfig, dnsName string, srvPort uint16, useTLS bool, mount, target, mds, grantHeaders string) error {
 	h := new(ipn.HTTPHandler)
 	switch {
 	case strings.HasPrefix(target, "text:"):
@@ -814,6 +815,9 @@ func (e *serveEnv) applyWebServe(sc *ipn.ServeConfig, dnsName string, srvPort ui
 			return err
 		}
 		h.Proxy = t
+		if grantHeaders != "" {
+			h.ForwardGrantHeaders = grantHeaders
+		}
 	}
 
 	// TODO: validation needs to check nested foreground configs

cmd/tailscale/cli/serve_v2_test.go

@@ -814,6 +814,25 @@ func TestServeDevConfigMutations(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "forward_grant_headers",
+			steps: []step{
+				{
+					command: cmd("serve --bg --forward-grant-headers=example.com/cap/grafana 3000"),
+					want: &ipn.ServeConfig{
+						TCP: map[uint16]*ipn.TCPPortHandler{443: {HTTPS: true}},
+						Web: map[ipn.HostPort]*ipn.WebServerConfig{
+							"foo.test.ts.net:443": {Handlers: map[string]*ipn.HTTPHandler{
+								"/": {
+									Proxy:               "http://127.0.0.1:3000",
+									ForwardGrantHeaders: "example.com/cap/grafana",
+								},
+							}},
+						},
+					},
+				},
+			},
+		},
 	}
 
 	for _, group := range groups {
@@ -1966,7 +1985,7 @@ func TestSetServe(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			err := e.setServe(tt.cfg, tt.dnsName, tt.srvType, tt.srvPort, tt.mountPath, tt.target, tt.allowFunnel, magicDNSSuffix)
+			err := e.setServe(tt.cfg, tt.dnsName, tt.srvType, tt.srvPort, tt.mountPath, tt.target, tt.allowFunnel, magicDNSSuffix, "")
 			if err != nil && !tt.expectErr {
 				t.Fatalf("got error: %v; did not expect error.", err)
 			}

ipn/ipn_clone.go

@@ -240,6 +240,7 @@ var _HTTPHandlerCloneNeedsRegeneration = HTTPHandler(struct {
 	Path                string
 	Proxy               string
 	Text                string
+	ForwardGrantHeaders string
 }{})
 
 // Clone makes a deep copy of WebServerConfig.

ipn/ipn_view.go

@@ -889,11 +889,15 @@ func (v HTTPHandlerView) Proxy() string { return v.ж.Proxy }
 // plaintext to serve (primarily for testing)
 func (v HTTPHandlerView) Text() string { return v.ж.Text }
 
+// name app capability to forward in grant headers
+func (v HTTPHandlerView) ForwardGrantHeaders() string { return v.ж.ForwardGrantHeaders }
+
 // A compilation failure here means this code must be regenerated, with the command at the top of this file.
 var _HTTPHandlerViewNeedsRegeneration = HTTPHandler(struct {
 	Path                string
 	Proxy               string
 	Text                string
+	ForwardGrantHeaders string
 }{})
 
 // View returns a read-only view of WebServerConfig.

ipn/ipnlocal/serve.go

@@ -60,6 +60,8 @@ type serveHTTPContext struct {
 
 	// provides funnel-specific context, nil if not funneled
 	Funnel *funnelFlow
+
+	ForwardGrantHeaders string
 }
 
 // funnelFlow represents a funneled connection initiated via IngressPeer
@@ -749,6 +751,7 @@ func (rp *reverseProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		r.Out.Host = r.In.Host
 		addProxyForwardedHeaders(r)
 		rp.lb.addTailscaleIdentityHeaders(r)
+		rp.lb.addCustomGrantHeaders(r)
 	}}
 
 	// There is no way to autodetect h2c as per RFC 9113
@@ -855,6 +858,27 @@ func (b *LocalBackend) addTailscaleIdentityHeaders(r *httputil.ProxyRequest) {
 	r.Out.Header.Set("Tailscale-Headers-Info", "https://tailscale.com/s/serve-headers")
 }
 
+func (b *LocalBackend) addCustomGrantHeaders(r *httputil.ProxyRequest) {
+	c, ok := serveHTTPContextKey.ValueOk(r.Out.Context())
+	if !ok {
+		return
+	}
+
+	peerCaps := b.PeerCaps(c.SrcAddr.Addr())
+	capToForward := tailcfg.PeerCapability(c.ForwardGrantHeaders)
+	cap, err := tailcfg.UnmarshalCapJSON[map[string]string](peerCaps, capToForward)
+	if err != nil {
+		b.logf("couldn't parse capability %s: %v", capToForward, err)
+		return
+	}
+	// take the first entry in the list for now
+	if len(cap) > 0 {
+		for k, v := range cap[0] {
+			r.Out.Header.Set(fmt.Sprintf("Tailscale-User-Capability-%s", k), encTailscaleHeaderValue(v))
+		}
+	}
+}
+
 // encTailscaleHeaderValue cleans or encodes as necessary v, to be suitable in
 // an HTTP header value. See
 // https://github.com/tailscale/tailscale/issues/11603.
@@ -893,6 +917,17 @@ func (b *LocalBackend) serveWebHandler(w http.ResponseWriter, r *http.Request) {
 			http.Error(w, "unknown proxy destination", http.StatusInternalServerError)
 			return
 		}
+		c, ok := serveHTTPContextKey.ValueOk(r.Context())
+		if !ok {
+			return
+		}
+		r = r.WithContext(serveHTTPContextKey.WithValue(r.Context(), &serveHTTPContext{
+			SrcAddr:             c.SrcAddr,
+			ForVIPService:       c.ForVIPService,
+			DestPort:            c.DestPort,
+			Funnel:              c.Funnel,
+			ForwardGrantHeaders: h.ForwardGrantHeaders(),
+		}))
 		h := p.(http.Handler)
 		// Trim the mount point from the URL path before proxying. (#6571)
 		if r.URL.Path != "/" {

ipn/ipnlocal/serve_test.go

@@ -24,6 +24,7 @@ import (
 	"testing"
 	"time"
 
+	"tailscale.com/control/controlclient"
 	"tailscale.com/health"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/store/mem"
@@ -37,6 +38,7 @@ import (
 	"tailscale.com/util/must"
 	"tailscale.com/util/syspolicy/policyclient"
 	"tailscale.com/wgengine"
+	"tailscale.com/wgengine/filter"
 )
 
 func TestExpandProxyArg(t *testing.T) {
@@ -758,6 +760,143 @@ func TestServeHTTPProxyHeaders(t *testing.T) {
 	}
 }
 
+func TestServeHTTPProxyHeadersForCustomGrants(t *testing.T) {
+	b := newTestBackend(t)
+
+	// Configure packet filter for custom app cap grant
+	// e.g.: "grants": [
+	//		{
+	//			"src": ["100.150.151.152"],
+	//			"dst": ["*"],
+	//			"app": {
+	//				"example.com/cap/grafana": [{
+	//					"role": "Admin",
+	//				}],
+	//			},
+	//		}
+	// ]
+	nm := b.NetMap()
+	matches, err := filter.MatchesFromFilterRules([]tailcfg.FilterRule{{
+		SrcIPs: []string{"100.150.151.152"},
+		CapGrant: []tailcfg.CapGrant{{
+			Dsts: []netip.Prefix{
+				netip.MustParsePrefix("100.150.151.151/32"),
+			},
+			CapMap: tailcfg.PeerCapMap{
+				"example.com/cap/grafana": []tailcfg.RawMessage{
+					"{\"role\": \"Admin\"}",
+				},
+			},
+		}},
+	}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	nm.PacketFilter = matches
+	b.SetControlClientStatus(nil, controlclient.Status{NetMap: nm})
+
+	// Start test serve endpoint.
+	testServ := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			// Piping all the headers through the response writer
+			// so we can check their values in tests below.
+			for key, val := range r.Header {
+				w.Header().Add(key, strings.Join(val, ","))
+			}
+		},
+	))
+	defer testServ.Close()
+
+	conf := &ipn.ServeConfig{
+		Web: map[ipn.HostPort]*ipn.WebServerConfig{
+			"example.ts.net:443": {Handlers: map[string]*ipn.HTTPHandler{
+				"/": {
+					Proxy:               testServ.URL,
+					ForwardGrantHeaders: "example.com/cap/grafana",
+				},
+			}},
+		},
+	}
+	if err := b.SetServeConfig(conf, ""); err != nil {
+		t.Fatal(err)
+	}
+
+	type headerCheck struct {
+		header string
+		want   string
+	}
+
+	tests := []struct {
+		name        string
+		srcIP       string
+		wantHeaders []headerCheck
+	}{
+		{
+			name:  "request-from-user-within-tailnet",
+			srcIP: "100.150.151.152",
+			wantHeaders: []headerCheck{
+				{"X-Forwarded-Proto", "https"},
+				{"X-Forwarded-For", "100.150.151.152"},
+				{"Tailscale-User-Login", "someone@example.com"},
+				{"Tailscale-User-Name", "Some One"},
+				{"Tailscale-User-Profile-Pic", "https://example.com/photo.jpg"},
+				{"Tailscale-Headers-Info", "https://tailscale.com/s/serve-headers"},
+				{"Tailscale-User-Capability-role", "Admin"},
+			},
+		},
+		{
+			name:  "request-from-tagged-node-within-tailnet",
+			srcIP: "100.150.151.153",
+			wantHeaders: []headerCheck{
+				{"X-Forwarded-Proto", "https"},
+				{"X-Forwarded-For", "100.150.151.153"},
+				{"Tailscale-User-Login", ""},
+				{"Tailscale-User-Name", ""},
+				{"Tailscale-User-Profile-Pic", ""},
+				{"Tailscale-Headers-Info", ""},
+				{"Tailscale-User-Capability-role", ""},
+			},
+		},
+		{
+			name:  "request-from-outside-tailnet",
+			srcIP: "100.160.161.162",
+			wantHeaders: []headerCheck{
+				{"X-Forwarded-Proto", "https"},
+				{"X-Forwarded-For", "100.160.161.162"},
+				{"Tailscale-User-Login", ""},
+				{"Tailscale-User-Name", ""},
+				{"Tailscale-User-Profile-Pic", ""},
+				{"Tailscale-Headers-Info", ""},
+				{"Tailscale-User-Capability-role", ""},
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := &http.Request{
+				URL: &url.URL{Path: "/"},
+				TLS: &tls.ConnectionState{ServerName: "example.ts.net"},
+			}
+			req = req.WithContext(serveHTTPContextKey.WithValue(req.Context(), &serveHTTPContext{
+				DestPort: 443,
+				SrcAddr:  netip.MustParseAddrPort(tt.srcIP + ":1234"), // random src port for tests
+			}))
+
+			w := httptest.NewRecorder()
+			b.serveWebHandler(w, req)
+
+			// Verify the headers.
+			h := w.Result().Header
+			for _, c := range tt.wantHeaders {
+				if got := h.Get(c.header); got != c.want {
+					t.Errorf("invalid %q header; want=%q, got=%q", c.header, c.want, got)
+				}
+			}
+		})
+	}
+}
+
 func Test_reverseProxyConfiguration(t *testing.T) {
 	b := newTestBackend(t)
 	type test struct {
@@ -916,6 +1055,9 @@ func newTestBackend(t *testing.T, opts ...any) *LocalBackend {
 	b.currentNode().SetNetMap(&netmap.NetworkMap{
 		SelfNode: (&tailcfg.Node{
 			Name: "example.ts.net",
+			Addresses: []netip.Prefix{
+				netip.MustParsePrefix("100.150.151.151/32"),
+			},
 		}).View(),
 		UserProfiles: map[tailcfg.UserID]tailcfg.UserProfileView{
 			tailcfg.UserID(1): (&tailcfg.UserProfile{

ipn/serve.go

@@ -160,6 +160,8 @@ type HTTPHandler struct {
 
 	Text string `json:",omitempty"` // plaintext to serve (primarily for testing)
 
+	ForwardGrantHeaders string `json:",omitempty"` // name app capability to forward in grant headers
+
 	// TODO(bradfitz): bool to not enumerate directories? TTL on mapping for
 	// temporary ones? Error codes? Redirects?
 }