[management, reverse proxy] Add reverse proxy feature (#5291)

* implement reverse proxy


---------

Co-authored-by: Alisdair MacLeod <git@alisdairmacleod.co.uk>
Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>
Co-authored-by: Eduard Gert <kontakt@eduardgert.de>
Co-authored-by: Viktor Liu <viktor@netbird.io>
Co-authored-by: Diego Noguês <diego.sure@gmail.com>
Co-authored-by: Diego Noguês <49420+diegocn@users.noreply.github.com>
Co-authored-by: Bethuel Mmbaga <bethuelmbaga12@gmail.com>
Co-authored-by: Zoltan Papp <zoltan.pmail@gmail.com>
Co-authored-by: Ashley Mensah <ashleyamo982@gmail.com>

proxy/trustedproxy_test.go

@@ -0,0 +1,90 @@
+package proxy
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseTrustedProxies(t *testing.T) {
+	tests := []struct {
+		name    string
+		raw     string
+		want    []netip.Prefix
+		wantErr bool
+	}{
+		{
+			name: "empty string returns nil",
+			raw:  "",
+			want: nil,
+		},
+		{
+			name: "single CIDR",
+			raw:  "10.0.0.0/8",
+			want: []netip.Prefix{netip.MustParsePrefix("10.0.0.0/8")},
+		},
+		{
+			name: "single bare IPv4",
+			raw:  "1.2.3.4",
+			want: []netip.Prefix{netip.MustParsePrefix("1.2.3.4/32")},
+		},
+		{
+			name: "single bare IPv6",
+			raw:  "::1",
+			want: []netip.Prefix{netip.MustParsePrefix("::1/128")},
+		},
+		{
+			name: "comma-separated CIDRs",
+			raw:  "10.0.0.0/8, 192.168.1.0/24",
+			want: []netip.Prefix{
+				netip.MustParsePrefix("10.0.0.0/8"),
+				netip.MustParsePrefix("192.168.1.0/24"),
+			},
+		},
+		{
+			name: "mixed CIDRs and bare IPs",
+			raw:  "10.0.0.0/8, 1.2.3.4, fd00::/8",
+			want: []netip.Prefix{
+				netip.MustParsePrefix("10.0.0.0/8"),
+				netip.MustParsePrefix("1.2.3.4/32"),
+				netip.MustParsePrefix("fd00::/8"),
+			},
+		},
+		{
+			name: "whitespace around entries",
+			raw:  "  10.0.0.0/8 , 192.168.0.0/16  ",
+			want: []netip.Prefix{
+				netip.MustParsePrefix("10.0.0.0/8"),
+				netip.MustParsePrefix("192.168.0.0/16"),
+			},
+		},
+		{
+			name: "trailing comma produces no extra entry",
+			raw:  "10.0.0.0/8,",
+			want: []netip.Prefix{netip.MustParsePrefix("10.0.0.0/8")},
+		},
+		{
+			name:    "invalid entry",
+			raw:     "not-an-ip",
+			wantErr: true,
+		},
+		{
+			name:    "partially invalid",
+			raw:     "10.0.0.0/8, garbage",
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ParseTrustedProxies(tt.raw)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}