diff --git a/CONTEXT.md b/CONTEXT.md
index 1e2fa0c..68f7349 100644
--- a/CONTEXT.md
+++ b/CONTEXT.md
@@ -1,6 +1,6 @@
 # go-nc-exapp
 
-Shared Go Library for Nextcloud ExApp Services: AppAPI authentication, OCS calls, and per-user ExApp preferences. ExApps import `gitea.neitzel.de/konrad/go-nc-exapp`. File storage and folder visits live in go-nc-files.
+Shared Go Library for Nextcloud ExApp Services: AppAPI authentication, OCS calls, per-user ExApp preferences, and optional Required Groups gating. ExApps import `gitea.neitzel.de/konrad/go-nc-exapp`. File storage and folder visits live in go-nc-files.
 
 ## Language
 
@@ -19,3 +19,11 @@ _Avoid_: settings file in User Files, instance-wide config
 **OCS**:
 Nextcloud's legacy HTTP API surface under `/ocs/v2.php/…`. This Library requests JSON responses (`format=json`) for machine-readable bodies.
 _Avoid_: assuming XML responses, REST-only Nextcloud APIs for ExApp prefs
+
+**Required Groups**:
+The Nextcloud groups configured for an ExApp (comma-separated deploy env `REQUIRED_GROUPS`) such that membership in any one of them is enough to use the ExApp. Empty or unset means no group restriction. AppAPI does not enforce this; the ExApp does.
+_Avoid_: AppAPI scopes, route access_level, admin-only top menu, treating the ExApp id as an implicit group name
+
+**Access Gate**:
+The Library check that enforces Required Groups for the Requesting user on ExApp HTTP traffic (403 or denied UI when not a member; 401 without a user; 503 when membership cannot be determined). Lifecycle paths stay ungated.
+_Avoid_: Nextcloud middleware, HaRP ACL, admin bypass
diff --git a/README.md b/README.md
index 00225ec..2fc0445 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,10 @@
 # go-nc-exapp
 
-Shared Go library for Nextcloud ExApp Services: AppAPI authentication, OCS JSON calls, and per-user ExApp preferences.
+Shared Go library for Nextcloud ExApp Services: AppAPI authentication, OCS JSON calls, per-user ExApp preferences, and optional Required Groups Access Gate.
 
 Import: `gitea.neitzel.de/konrad/go-nc-exapp`
 
-## v1 scope
+## Scope
 
 **Included**
 
@@ -14,10 +14,11 @@ Import: `gitea.neitzel.de/konrad/go-nc-exapp`
 - **UserFromRequest** — extract the requesting user from inbound AppAPI-proxied requests
 - **OCSClient** — authenticated OCS calls that always append `format=json`
 - **AppAPIPreferences** — parameterized get/set of a string ExApp preference (caller supplies app id and key)
+- **Access Gate** — optional Required Groups enforcement (`Wrap` + `Check`), English denied HTML, positive membership cache; env helpers for `REQUIRED_GROUPS` / `REQUIRED_GROUPS_CACHE_SECONDS`
 
-**Excluded from v1**
+**Excluded**
 
-- ExApp lifecycle HTTP routes (`/heartbeat`, `/enabled`, …)
+- ExApp lifecycle HTTP routes (`/heartbeat`, `/enabled`, …) — the Gate *skips* these by default but does not implement them
 - HaRP listen / `serve()` and unix-socket bootstrap
 - Top-menu, script, and iframe UI registration
 - WebDAV and file storage (see **go-nc-files**)
@@ -37,15 +38,23 @@ cred := gonexapp.Credentials{
 
 prefs := gonexapp.NewAppAPIPreferences(cred, "myexapp", "savedDefault")
 value, err := prefs.Get()
+
+groupsEnv, groupsSet := os.LookupEnv("REQUIRED_GROUPS")
+groups := gonexapp.ResolveRequiredGroups(groupsEnv, groupsSet, nil)
+ttl := gonexapp.ParseCacheSeconds(os.Getenv("REQUIRED_GROUPS_CACHE_SECONDS"), gonexapp.DefaultCacheSeconds)
+handler := gonexapp.AccessGate{Cred: cred, Groups: groups, CacheTTL: ttl}.Wrap(inner)
 ```
 
 Each ExApp chooses its own preference keys; this library does not hardcode product-specific names.
 
+Declare `REQUIRED_GROUPS` and `REQUIRED_GROUPS_CACHE_SECONDS` in the ExApp `info.xml` so Deploy options can set them.
+
 ## Domain language
 
-See [CONTEXT.md](./CONTEXT.md) for AppAPI credentials, requesting user, ExApp preference, and OCS terminology.
+See [CONTEXT.md](./CONTEXT.md) for AppAPI credentials, Requesting user, ExApp preference, OCS, Required Groups, and Access Gate terminology.
 
 ## Related
 
 - **go-nc-files** — WebDAV, Working Folder, Saved Default, Visit resolution
 - Workspace ADR 0013 — extraction from CheckDNS
+- Workspace ADR `docs/adr/go-nc-exapp/0001-required-groups-access-gate.md` — Access Gate decisions
diff --git a/access_gate.go b/access_gate.go
new file mode 100644
index 0000000..29cf92b
--- /dev/null
+++ b/access_gate.go
@@ -0,0 +1,216 @@
+package gonexapp
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+)
+
+// AccessGate enforces Required Groups for the Requesting user on ExApp HTTP traffic.
+type AccessGate struct {
+	Cred           Credentials
+	Groups         []string
+	CacheTTL       time.Duration // 0 disables cache
+	ExtraSkipPaths []string
+	Client         *http.Client
+	OCS            OCSClient
+	Now            func() time.Time
+
+	mu    sync.Mutex
+	cache map[string]cacheEntry
+}
+
+type cacheEntry struct {
+	until time.Time
+}
+
+// CheckResult is the outcome of AccessGate.Check.
+type CheckResult int
+
+const (
+	CheckAllowed CheckResult = iota
+	CheckDenied
+	CheckUnauthorized
+	CheckUnavailable
+)
+
+// Wrap returns a handler that applies the Access Gate before next.
+func (g AccessGate) Wrap(next http.Handler) http.Handler {
+	gate := g.normalized()
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch gate.Check(r) {
+		case CheckAllowed:
+			next.ServeHTTP(w, r)
+		case CheckUnauthorized:
+			http.Error(w, "unauthorized", http.StatusUnauthorized)
+		case CheckUnavailable:
+			http.Error(w, "service unavailable", http.StatusServiceUnavailable)
+		default:
+			gate.writeDenied(w, r)
+		}
+	})
+}
+
+// Check reports whether r may proceed under Required Groups.
+func (g *AccessGate) Check(r *http.Request) CheckResult {
+	if g.cache == nil {
+		g.cache = make(map[string]cacheEntry)
+	}
+	if g.Now == nil {
+		g.Now = time.Now
+	}
+	if g.shouldSkip(r.URL.Path) || len(g.Groups) == 0 {
+		return CheckAllowed
+	}
+	user, err := UserFromRequest(r)
+	if err != nil || user == "" {
+		return CheckUnauthorized
+	}
+	ok, err := g.memberOfRequired(user)
+	if err != nil {
+		return CheckUnavailable
+	}
+	if ok {
+		return CheckAllowed
+	}
+	return CheckDenied
+}
+
+func (g *AccessGate) memberOfRequired(userID string) (bool, error) {
+	if g.CacheTTL > 0 {
+		if g.cachedAllowed(userID) {
+			return true, nil
+		}
+	}
+	groups, err := g.fetchUserGroups(userID)
+	if err != nil {
+		return false, err
+	}
+	for _, need := range g.Groups {
+		for _, have := range groups {
+			if have == need {
+				if g.CacheTTL > 0 {
+					g.storeAllowed(userID)
+				}
+				return true, nil
+			}
+		}
+	}
+	return false, nil
+}
+
+func (g *AccessGate) fetchUserGroups(userID string) ([]string, error) {
+	ocs := g.ocsClient(userID)
+	path := "cloud/users/" + url.PathEscape(userID) + "/groups"
+	raw, err := ocs.Call(http.MethodGet, path, nil)
+	if err != nil {
+		return nil, err
+	}
+	return decodeUserGroups(raw)
+}
+
+func (g *AccessGate) ocsClient(userID string) OCSClient {
+	c := g.OCS
+	if c.Cred.BaseURL == "" {
+		c.Cred = g.Cred
+	}
+	c.Cred = c.Cred.WithUser(userID)
+	if c.Client == nil {
+		c.Client = g.Client
+	}
+	return c
+}
+
+func decodeUserGroups(raw []byte) ([]string, error) {
+	var parsed struct {
+		OCS struct {
+			Data struct {
+				Groups []string `json:"groups"`
+			} `json:"data"`
+		} `json:"ocs"`
+	}
+	if err := json.Unmarshal(raw, &parsed); err != nil {
+		return nil, fmt.Errorf("user groups decode: %w", err)
+	}
+	return parsed.OCS.Data.Groups, nil
+}
+
+func (g *AccessGate) cachedAllowed(userID string) bool {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	ent, ok := g.cache[userID]
+	if !ok {
+		return false
+	}
+	if g.Now().After(ent.until) {
+		delete(g.cache, userID)
+		return false
+	}
+	return true
+}
+
+func (g *AccessGate) storeAllowed(userID string) {
+	g.mu.Lock()
+	defer g.mu.Unlock()
+	g.cache[userID] = cacheEntry{until: g.Now().Add(g.CacheTTL)}
+}
+
+func (g AccessGate) normalized() *AccessGate {
+	out := g
+	if out.cache == nil {
+		out.cache = make(map[string]cacheEntry)
+	}
+	if out.Now == nil {
+		out.Now = time.Now
+	}
+	return &out
+}
+
+func (g *AccessGate) writeDenied(w http.ResponseWriter, r *http.Request) {
+	if acceptsHTML(r.Header.Get("Accept")) {
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.WriteHeader(http.StatusForbidden)
+		_, _ = w.Write(deniedHTML)
+		return
+	}
+	http.Error(w, "forbidden", http.StatusForbidden)
+}
+
+func acceptsHTML(accept string) bool {
+	return strings.Contains(strings.ToLower(accept), "text/html")
+}
+
+func (g *AccessGate) shouldSkip(path string) bool {
+	path = strings.TrimSuffix(path, "/")
+	if path == "" {
+		path = "/"
+	}
+	for _, p := range defaultSkipPaths {
+		if path == p {
+			return true
+		}
+	}
+	for _, p := range g.ExtraSkipPaths {
+		p = strings.TrimSuffix(p, "/")
+		if p == "" {
+			p = "/"
+		}
+		if path == p {
+			return true
+		}
+	}
+	return false
+}
+
+var defaultSkipPaths = []string{"/heartbeat", "/enabled", "/init"}
+
+var deniedHTML = []byte(`<!DOCTYPE html>
+<html lang="en">
+<head><meta charset="utf-8"><title>Access denied</title></head>
+<body><h1>Access denied</h1><p>You are not a member of a required group for this app.</p></body>
+</html>
+`)
diff --git a/access_gate_test.go b/access_gate_test.go
new file mode 100644
index 0000000..e12aea3
--- /dev/null
+++ b/access_gate_test.go
@@ -0,0 +1,359 @@
+package gonexapp_test
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"gitea.neitzel.de/konrad/go-nc-exapp"
+)
+
+func authHeader(userID string) string {
+	return base64.StdEncoding.EncodeToString([]byte(userID + ":secret"))
+}
+
+func okInner() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		_, _ = io.WriteString(w, "ok")
+	})
+}
+
+func TestAccessGateEmptyGroupsPassesThrough(t *testing.T) {
+	gate := gonexapp.AccessGate{}
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK || rec.Body.String() != "ok" {
+		t.Fatalf("got %d %q", rec.Code, rec.Body.String())
+	}
+}
+
+func TestAccessGateSkipsLifecyclePaths(t *testing.T) {
+	gate := gonexapp.AccessGate{Groups: []string{"dns-ops"}}
+	h := gate.Wrap(okInner())
+
+	for _, path := range []string{"/heartbeat", "/enabled", "/init"} {
+		req := httptest.NewRequest(http.MethodGet, path, nil)
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		if rec.Code != http.StatusOK {
+			t.Fatalf("%s: got %d", path, rec.Code)
+		}
+	}
+}
+
+func TestAccessGateExtraSkipPaths(t *testing.T) {
+	gate := gonexapp.AccessGate{Groups: []string{"dns-ops"}, ExtraSkipPaths: []string{"/healthz"}}
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/healthz", nil)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("got %d", rec.Code)
+	}
+}
+
+func TestAccessGateMissingUserUnauthorized(t *testing.T) {
+	gate := gonexapp.AccessGate{Groups: []string{"dns-ops"}}
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("got %d", rec.Code)
+	}
+}
+
+func groupsOCSServer(t *testing.T, handler http.HandlerFunc) *httptest.Server {
+	t.Helper()
+	srv := httptest.NewServer(handler)
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+func gateWithOCS(t *testing.T, groups []string, ttl time.Duration, srv *httptest.Server) gonexapp.AccessGate {
+	t.Helper()
+	cred := gonexapp.Credentials{
+		BaseURL: srv.URL, AppID: "app", AppVersion: "0.1.0", AAVersion: "1.0.0", AppSecret: "s",
+	}
+	return gonexapp.AccessGate{
+		Cred:     cred,
+		Groups:   groups,
+		CacheTTL: ttl,
+		Client:   srv.Client(),
+		OCS:      gonexapp.OCSClient{Cred: cred, Client: srv.Client()},
+	}
+}
+
+func TestAccessGateAllowsAnyOfMember(t *testing.T) {
+	var calls atomic.Int32
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		calls.Add(1)
+		if r.Method != http.MethodGet || !strings.Contains(r.URL.Path, "/cloud/users/alice/groups") {
+			http.Error(w, "bad path "+r.URL.Path, http.StatusBadRequest)
+			return
+		}
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"other", "dns-ops"}}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops", "dns-admins"}, 0, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK || rec.Body.String() != "ok" {
+		t.Fatalf("got %d %q", rec.Code, rec.Body.String())
+	}
+	if calls.Load() != 1 {
+		t.Fatalf("ocs calls=%d", calls.Load())
+	}
+}
+
+func TestAccessGateDeniesNonMemberWith403(t *testing.T) {
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"users"}}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, 0, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusForbidden {
+		t.Fatalf("got %d", rec.Code)
+	}
+	if strings.Contains(rec.Header().Get("Content-Type"), "text/html") {
+		t.Fatalf("unexpected html content-type")
+	}
+}
+
+func TestAccessGateDeniesNonMemberWithHTML(t *testing.T) {
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"users"}}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, 0, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	req.Header.Set("Accept", "text/html,application/xhtml+xml")
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusForbidden {
+		t.Fatalf("got %d", rec.Code)
+	}
+	if !strings.Contains(rec.Header().Get("Content-Type"), "text/html") {
+		t.Fatalf("content-type=%q", rec.Header().Get("Content-Type"))
+	}
+	if !strings.Contains(rec.Body.String(), "Access denied") {
+		t.Fatalf("body=%q", rec.Body.String())
+	}
+}
+
+func TestAccessGateLookupFailureServiceUnavailable(t *testing.T) {
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "boom", http.StatusInternalServerError)
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, 0, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusServiceUnavailable {
+		t.Fatalf("got %d", rec.Code)
+	}
+}
+
+func TestAccessGateCachesPositiveMembership(t *testing.T) {
+	var calls atomic.Int32
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		calls.Add(1)
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"dns-ops"}}},
+		})
+	})
+	now := time.Unix(1_700_000_000, 0)
+	gate := gateWithOCS(t, []string{"dns-ops"}, time.Minute, srv)
+	gate.Now = func() time.Time { return now }
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	for i := 0; i < 2; i++ {
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		if rec.Code != http.StatusOK {
+			t.Fatalf("pass %d: got %d", i, rec.Code)
+		}
+	}
+	if calls.Load() != 1 {
+		t.Fatalf("ocs calls=%d want 1", calls.Load())
+	}
+}
+
+func TestAccessGateDoesNotCacheDenial(t *testing.T) {
+	var calls atomic.Int32
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		n := calls.Add(1)
+		groups := []string{"users"}
+		if n >= 2 {
+			groups = []string{"dns-ops"}
+		}
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": groups}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, time.Minute, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusForbidden {
+		t.Fatalf("first: got %d", rec.Code)
+	}
+
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("second: got %d", rec.Code)
+	}
+	if calls.Load() != 2 {
+		t.Fatalf("ocs calls=%d want 2", calls.Load())
+	}
+}
+
+func TestAccessGateZeroTTLDisablesCache(t *testing.T) {
+	var calls atomic.Int32
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		calls.Add(1)
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"dns-ops"}}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, 0, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	for i := 0; i < 2; i++ {
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		if rec.Code != http.StatusOK {
+			t.Fatalf("pass %d: got %d", i, rec.Code)
+		}
+	}
+	if calls.Load() != 2 {
+		t.Fatalf("ocs calls=%d want 2", calls.Load())
+	}
+}
+
+func TestAccessGateDoesNotCacheLookupErrors(t *testing.T) {
+	var calls atomic.Int32
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		n := calls.Add(1)
+		if n == 1 {
+			http.Error(w, "boom", http.StatusInternalServerError)
+			return
+		}
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"dns-ops"}}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, time.Minute, srv)
+	h := gate.Wrap(okInner())
+
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusServiceUnavailable {
+		t.Fatalf("first: got %d", rec.Code)
+	}
+
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("second: got %d", rec.Code)
+	}
+}
+
+func TestParseRequiredGroups(t *testing.T) {
+	got := gonexapp.ParseRequiredGroups(" dns-ops, dns-admins ,, ")
+	if len(got) != 2 || got[0] != "dns-ops" || got[1] != "dns-admins" {
+		t.Fatalf("got %#v", got)
+	}
+	if len(gonexapp.ParseRequiredGroups("")) != 0 {
+		t.Fatalf("empty should be empty")
+	}
+}
+
+func TestResolveRequiredGroups(t *testing.T) {
+	def := []string{"checkdns"}
+	if got := gonexapp.ResolveRequiredGroups("", false, def); len(got) != 1 || got[0] != "checkdns" {
+		t.Fatalf("unset: %#v", got)
+	}
+	if got := gonexapp.ResolveRequiredGroups("", true, def); len(got) != 0 {
+		t.Fatalf("set empty: %#v", got)
+	}
+	if got := gonexapp.ResolveRequiredGroups("ops", true, def); len(got) != 1 || got[0] != "ops" {
+		t.Fatalf("set: %#v", got)
+	}
+}
+
+func TestParseCacheSeconds(t *testing.T) {
+	if d := gonexapp.ParseCacheSeconds("", 60); d != 60*time.Second {
+		t.Fatalf("default unset: %v", d)
+	}
+	if d := gonexapp.ParseCacheSeconds("0", 60); d != 0 {
+		t.Fatalf("zero: %v", d)
+	}
+	if d := gonexapp.ParseCacheSeconds("30", 60); d != 30*time.Second {
+		t.Fatalf("thirty: %v", d)
+	}
+	if d := gonexapp.ParseCacheSeconds("nope", 60); d != 60*time.Second {
+		t.Fatalf("invalid: %v", d)
+	}
+}
+
+func TestAccessGateCheckStandalone(t *testing.T) {
+	srv := groupsOCSServer(t, func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"ocs": map[string]any{"data": map[string]any{"groups": []string{"dns-ops"}}},
+		})
+	})
+	gate := gateWithOCS(t, []string{"dns-ops"}, 0, srv)
+	ptr := &gonexapp.AccessGate{
+		Cred: gate.Cred, Groups: gate.Groups, CacheTTL: gate.CacheTTL, Client: gate.Client, OCS: gate.OCS,
+	}
+	req := httptest.NewRequest(http.MethodGet, "/api/zones", nil)
+	req.Header.Set("AUTHORIZATION-APP-API", authHeader("alice"))
+	if got := ptr.Check(req); got != gonexapp.CheckAllowed {
+		t.Fatalf("got %v", got)
+	}
+}
diff --git a/doc.go b/doc.go
index f20fce2..767f281 100644
--- a/doc.go
+++ b/doc.go
@@ -1,3 +1,3 @@
-// Package gonexapp provides AppAPI credentials, OCS JSON calls, and ExApp user
-// preferences for Nextcloud ExApp Services.
+// Package gonexapp provides AppAPI credentials, OCS JSON calls, ExApp user
+// preferences, and an optional Required Groups Access Gate for Nextcloud ExApp Services.
 package gonexapp
diff --git a/required_groups_env.go b/required_groups_env.go
new file mode 100644
index 0000000..4c444c9
--- /dev/null
+++ b/required_groups_env.go
@@ -0,0 +1,51 @@
+package gonexapp
+
+import (
+	"strconv"
+	"strings"
+	"time"
+)
+
+// EnvRequiredGroups is the conventional deploy env name for Required Groups.
+const EnvRequiredGroups = "REQUIRED_GROUPS"
+
+// EnvRequiredGroupsCacheSeconds is the conventional deploy env name for Access Gate cache TTL.
+const EnvRequiredGroupsCacheSeconds = "REQUIRED_GROUPS_CACHE_SECONDS"
+
+// DefaultCacheSeconds is used when REQUIRED_GROUPS_CACHE_SECONDS is unset or invalid.
+const DefaultCacheSeconds = 60
+
+// ParseRequiredGroups splits a comma-separated Required Groups env value.
+func ParseRequiredGroups(s string) []string {
+	parts := strings.Split(s, ",")
+	out := make([]string, 0, len(parts))
+	for _, p := range parts {
+		p = strings.TrimSpace(p)
+		if p == "" {
+			continue
+		}
+		out = append(out, p)
+	}
+	return out
+}
+
+// ResolveRequiredGroups applies env override rules: unset uses codeDefault;
+// set (including empty) replaces the default.
+func ResolveRequiredGroups(envValue string, envSet bool, codeDefault []string) []string {
+	if !envSet {
+		return append([]string(nil), codeDefault...)
+	}
+	return ParseRequiredGroups(envValue)
+}
+
+// ParseCacheSeconds parses REQUIRED_GROUPS_CACHE_SECONDS. Unset or invalid → defaultSec seconds; "0" → no cache.
+func ParseCacheSeconds(s string, defaultSec int) time.Duration {
+	if strings.TrimSpace(s) == "" {
+		return time.Duration(defaultSec) * time.Second
+	}
+	n, err := strconv.Atoi(strings.TrimSpace(s))
+	if err != nil || n < 0 {
+		return time.Duration(defaultSec) * time.Second
+	}
+	return time.Duration(n) * time.Second
+}