client/web: extract web client from cli package

move the tailscale web client out of the cmd/tailscale/cli package, into
a new client/web package.  The remaining cli/web.go file is still
responsible for parsing CLI flags and such, and then calls into
client/web. This will allow the web client to be hooked into from other
contexts (for example, from a tsnet server), and provide a dedicated
space to add more functionality to this client.

Updates tailscale/corp#13775

Signed-off-by: Will Norris <will@tailscale.com>

client/web/web_test.go

@@ -0,0 +1,64 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package web
+
+import (
+	"net/url"
+	"testing"
+)
+
+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)
+			}
+		})
+	}
+}