[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>

management/internals/modules/reverseproxy/domain/validator_test.go

@@ -0,0 +1,56 @@
+package domain_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/netbirdio/netbird/management/internals/modules/reverseproxy/domain"
+)
+
+type resolver struct {
+	CNAME string
+}
+
+func (r resolver) LookupCNAME(_ context.Context, _ string) (string, error) {
+	return r.CNAME, nil
+}
+
+func TestIsValid(t *testing.T) {
+	tests := map[string]struct {
+		resolver interface {
+			LookupCNAME(context.Context, string) (string, error)
+		}
+		domain string
+		accept []string
+		expect bool
+	}{
+		"match": {
+			resolver: resolver{"bar.example.com."}, // Including trailing "." in response.
+			domain:   "foo.example.com",
+			accept:   []string{"bar.example.com"},
+			expect:   true,
+		},
+		"no match": {
+			resolver: resolver{"invalid"},
+			domain:   "foo.example.com",
+			accept:   []string{"bar.example.com"},
+			expect:   false,
+		},
+		"accept trailing dot": {
+			resolver: resolver{"bar.example.com."},
+			domain:   "foo.example.com",
+			accept:   []string{"bar.example.com."}, // Including trailing "." in accept.
+			expect:   true,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			validator := domain.NewValidator(test.resolver)
+			actual := validator.IsValid(t.Context(), test.domain, test.accept)
+			if test.expect != actual {
+				t.Errorf("Incorrect return value:\nexpect: %v\nactual: %v", test.expect, actual)
+			}
+		})
+	}
+}