cmd/tailscale: use request Schema+Host for QNAP authLogin.cgi

QNAP allows users to set the port number for the management WebUI,
which includes authLogin.cgi. If they do, then connecting to
localhost:8080 fails.

https://github.com/tailscale/tailscale-qpkg/issues/74#issuecomment-1407486911

Fixes https://github.com/tailscale/tailscale/issues/7108

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

cmd/tailscale/cli/web.go

@@ -228,33 +228,48 @@ func qnapAuthn(r *http.Request) (string, *qnapAuthResponse, error) {
 	return "", nil, fmt.Errorf("not authenticated by any mechanism")
 }
 
-func qnapAuthnQtoken(r *http.Request, user, token string) (string, *qnapAuthResponse, error) {
-	query := url.Values{
-		"qtoken": []string{token},
-		"user":   []string{user},
+// qnapAuthnURL returns the auth URL to use by inferring where the UI is
+// running based on the request URL. This is necessary because QNAP has so
+// many options, see https://github.com/tailscale/tailscale/issues/7108
+// and https://github.com/tailscale/tailscale/issues/6903
+func qnapAuthnURL(requestUrl string, query url.Values) string {
+	in, err := url.Parse(requestUrl)
+	scheme := ""
+	host := ""
+	if err != nil || in.Scheme == "" {
+		log.Printf("Cannot parse QNAP login URL %v", err)
+
+		// try localhost and hope for the best
+		scheme = "http"
+		host = "localhost"
+	} else {
+		scheme = in.Scheme
+		host = in.Host
 	}
+
 	u := url.URL{
-		Scheme:   "http",
-		Host:     "127.0.0.1:8080",
+		Scheme:   scheme,
+		Host:     host,
 		Path:     "/cgi-bin/authLogin.cgi",
 		RawQuery: query.Encode(),
 	}
 
-	return qnapAuthnFinish(user, u.String())
+	return u.String()
+}
+
+func qnapAuthnQtoken(r *http.Request, user, token string) (string, *qnapAuthResponse, error) {
+	query := url.Values{
+		"qtoken": []string{token},
+		"user":   []string{user},
+	}
+	return qnapAuthnFinish(user, qnapAuthnURL(r.URL.String(), query))
 }
 
 func qnapAuthnSid(r *http.Request, user, sid string) (string, *qnapAuthResponse, error) {
 	query := url.Values{
 		"sid": []string{sid},
 	}
-	u := url.URL{
-		Scheme:   "http",
-		Host:     "127.0.0.1:8080",
-		Path:     "/cgi-bin/authLogin.cgi",
-		RawQuery: query.Encode(),
-	}
-
-	return qnapAuthnFinish(user, u.String())
+	return qnapAuthnFinish(user, qnapAuthnURL(r.URL.String(), query))
 }
 
 func qnapAuthnFinish(user, url string) (string, *qnapAuthResponse, error) {

cmd/tailscale/cli/web_test.go

@@ -3,7 +3,10 @@
 
 package cli
 
-import "testing"
+import (
+	"net/url"
+	"testing"
+)
 
 func TestUrlOfListenAddr(t *testing.T) {
 	tests := []struct {
@@ -34,9 +37,65 @@ func TestUrlOfListenAddr(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			url := urlOfListenAddr(tt.in)
-			if url != tt.want {
-				t.Errorf("expected url: %q, got: %q", tt.want, url)
+			u := urlOfListenAddr(tt.in)
+			if u != tt.want {
+				t.Errorf("expected url: %q, got: %q", tt.want, u)
+			}
+		})
+	}
+}
+
+func TestQnapAuthnURL(t *testing.T) {
+	query := url.Values{
+		"qtoken": []string{"token"},
+	}
+	tests := []struct {
+		name string
+		in   string
+		want string
+	}{
+		{
+			name: "localhost http",
+			in:   "http://localhost:8088/",
+			want: "http://localhost:8088/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+		{
+			name: "localhost https",
+			in:   "https://localhost:5000/",
+			want: "https://localhost:5000/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+		{
+			name: "IP http",
+			in:   "http://10.1.20.4:80/",
+			want: "http://10.1.20.4:80/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+		{
+			name: "IP6 https",
+			in:   "https://[ff7d:0:1:2::1]/",
+			want: "https://[ff7d:0:1:2::1]/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+		{
+			name: "hostname https",
+			in:   "https://qnap.example.com/",
+			want: "https://qnap.example.com/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+		{
+			name: "invalid URL",
+			in:   "This is not a URL, it is a really really really really really really really really really really really really long string to exercise the URL truncation code in the error path.",
+			want: "http://localhost/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+		{
+			name: "err != nil",
+                        in:   "http://192.168.0.%31/",
+			want: "http://localhost/cgi-bin/authLogin.cgi?qtoken=token",
+		},
+
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			u := qnapAuthnURL(tt.in, query)
+			if u != tt.want {
+				t.Errorf("expected url: %q, got: %q", tt.want, u)
 			}
 		})
 	}