Add per-role HTTP method scoping to minted tokens

Every token this engine mints is as powerful as the apps it can reach: a
read-only integration can still write to the *arr. arrproxy v0.5.0 accepts
a method scope at mint time, so let a role pin its tokens to it.

- Add an optional role field methods, uppercase-normalized, de-duplicated
  and validated against the known HTTP methods at role write.
- Forward the role's scope as methods on the arrproxy mint request and
  echo it in the creds response alongside apps/subject.
- Omit the field entirely when a role has no scope, so an arrproxy
  predating method scoping sees an unchanged request.
- Cover normalization, rejection, pass-through and the unscoped case.

README.md

@@ -13,6 +13,8 @@ bearer-gated **admin API** (`/api/admin/tokens`) instead, so Terraform-driven
 Each minted token is:
 
 - **scoped to a subset of apps** (`apps`: any of `sonarr`, `radarr`, `prowlarr`)
+- **optionally scoped to HTTP methods** (`methods`, e.g. `GET,HEAD` for a
+  read-only consumer; empty means unrestricted)
 - **subject-namespaced** as `vault:arrstack:<role>` (arrproxy requires the prefix)
 - **bound to a Vault lease** — revoking the lease disables the token in arrproxy
 
@@ -49,6 +51,7 @@ vault write arrstack/config \
   ca_cert=@traefik-external-ca.pem   # optional
 
 # 3. Define a role: which apps, what TTLs
+#    (add methods="GET,HEAD" to pin the token to those HTTP methods)
 vault write arrstack/roles/media \
   apps="sonarr,radarr" \
   ttl=1h \
@@ -61,6 +64,7 @@ vault read arrstack/creds/media
 # lease_id      arrstack/creds/media/AbC...
 # lease_duration 1h
 # apps          [radarr sonarr]
+# methods       []
 # id            tok-...
 # subject       vault:arrstack:media
 # token         arr_...
@@ -108,9 +112,30 @@ vault write arrstack/roles/all      apps="sonarr,radarr,prowlarr"   ttl=1h max_t
 | Field     | Type     | Description                                                         |
 | --------- | -------- | ------------------------------------------------------------------ |
 | `apps`    | list     | Non-empty subset of `sonarr`/`radarr`/`prowlarr`                   |
+| `methods` | list     | Optional HTTP methods the token is limited to; empty = unrestricted |
 | `ttl`     | duration | Default lease TTL                                                   |
 | `max_ttl` | duration | Maximum lease TTL                                                   |
 
+## Method scoping
+
+A role may pin its tokens to a set of HTTP methods, so a read-only integration
+cannot write to the *arr even on an app it is allowed to reach. Entries are
+uppercase-normalized and must name one of `GET`, `HEAD`, `POST`, `PUT`,
+`PATCH`, `DELETE`, `OPTIONS` — an unknown method is rejected at role write, not
+at mint. The scope is sent to arrproxy at mint time and enforced there: a
+request outside it is refused with `405` before any upstream *arr is reached.
+
+Leaving `methods` unset (the default) leaves the token unrestricted, exactly as
+before this field existed.
+
+```sh
+# A token that can read Sonarr but never change it.
+vault write arrstack/roles/sonarr-ro apps="sonarr" methods="GET,HEAD" ttl=1h max_ttl=24h
+
+# Drop the scope again on an existing role.
+vault write arrstack/roles/sonarr-ro methods=""
+```
+
 ## TTL and renewal
 
 At mint time the effective initial lease TTL is sent to arrproxy as

backend_test.go

@@ -3,6 +3,7 @@ package arrstack
 import (
 	"context"
 	"encoding/json"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"strconv"
@@ -33,6 +34,7 @@ func getTestBackend(t *testing.T) (*arrstackBackend, logical.Storage) {
 type mockToken struct {
 	Subject   string
 	Apps      []string
+	Methods   []string
 	Label     string
 	ExpiresAt *time.Time
 	Disabled  bool
@@ -49,9 +51,13 @@ type mockArrproxy struct {
 	counter    int
 	adminToken string
 	apps       map[string]bool
+	methods    map[string]bool
 
-	mintErr     bool
+	mintErr bool
+	// lastRequest is the decoded mint payload; lastBody is the raw JSON, so a
+	// test can assert a field was omitted rather than sent empty.
 	lastRequest mintTokenRequest
+	lastBody    []byte
 }
 
 func newMockArrproxy(t *testing.T) *mockArrproxy {
@@ -60,6 +66,10 @@ func newMockArrproxy(t *testing.T) *mockArrproxy {
 		tokens:     make(map[string]*mockToken),
 		adminToken: "arrproxy-admin-secret",
 		apps:       map[string]bool{"sonarr": true, "radarr": true, "prowlarr": true},
+		methods: map[string]bool{
+			"GET": true, "HEAD": true, "POST": true, "PUT": true,
+			"PATCH": true, "DELETE": true, "OPTIONS": true,
+		},
 	}
 
 	mux := http.NewServeMux()
@@ -108,12 +118,18 @@ func (m *mockArrproxy) handleMint(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	body, err := io.ReadAll(r.Body)
+	if err != nil {
+		http.Error(w, "bad request", http.StatusBadRequest)
+		return
+	}
 	var req mintTokenRequest
-	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+	if err := json.Unmarshal(body, &req); err != nil {
 		http.Error(w, "bad request", http.StatusBadRequest)
 		return
 	}
 	m.lastRequest = req
+	m.lastBody = body
 
 	if !strings.HasPrefix(req.Subject, "vault:arrstack:") || strings.TrimSpace(strings.TrimPrefix(req.Subject, "vault:arrstack:")) == "" {
 		http.Error(w, "subject must be namespaced with vault:arrstack:", http.StatusBadRequest)
@@ -129,6 +145,13 @@ func (m *mockArrproxy) handleMint(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 	}
+	// An absent or empty methods list is unrestricted.
+	for _, meth := range req.Methods {
+		if !m.methods[meth] {
+			http.Error(w, "methods must name known HTTP methods", http.StatusBadRequest)
+			return
+		}
+	}
 	if req.TTLSeconds < 0 {
 		http.Error(w, "ttl_seconds must not be negative", http.StatusBadRequest)
 		return
@@ -141,9 +164,14 @@ func (m *mockArrproxy) handleMint(w http.ResponseWriter, r *http.Request) {
 		exp := time.Now().UTC().Add(time.Duration(req.TTLSeconds) * time.Second)
 		expiresAt = &exp
 	}
+	methods := req.Methods
+	if methods == nil {
+		methods = []string{}
+	}
 	m.tokens[id] = &mockToken{
 		Subject:   req.Subject,
 		Apps:      req.Apps,
+		Methods:   methods,
 		Label:     req.Label,
 		ExpiresAt: expiresAt,
 	}
@@ -151,6 +179,7 @@ func (m *mockArrproxy) handleMint(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusCreated, map[string]interface{}{
 		"id":         id,
 		"token":      "arr_" + id + "_plaintext",
+		"methods":    methods,
 		"expires_at": expiresAt,
 	})
 }

client.go

@@ -63,8 +63,11 @@ func newClient(config *arrstackConfig) (*arrproxyClient, error) {
 // mintTokenRequest is the payload for POST /api/admin/tokens. The subject MUST
 // carry the "vault:arrstack:" prefix or arrproxy rejects the request.
 type mintTokenRequest struct {
-	Subject    string   `json:"subject"`
-	Apps       []string `json:"apps"`
+	Subject string   `json:"subject"`
+	Apps    []string `json:"apps"`
+	// Methods limits the token to those HTTP methods. Omitted when empty so
+	// arrproxy versions predating method scoping see the request unchanged.
+	Methods    []string `json:"methods,omitempty"`
 	Label      string   `json:"label"`
 	TTLSeconds int64    `json:"ttl_seconds"`
 }

client_test.go

@@ -2,6 +2,7 @@ package arrstack
 
 import (
 	"context"
+	"strings"
 	"testing"
 )
 
@@ -35,6 +36,38 @@ func TestClient_MintToken(t *testing.T) {
 	}
 }
 
+func TestClient_MintToken_ForwardsMethods(t *testing.T) {
+	m := newMockArrproxy(t)
+	client, _ := newClient(&arrstackConfig{BaseURL: m.server.URL, AdminToken: m.adminToken})
+
+	if _, err := client.MintToken(context.Background(), mintTokenRequest{
+		Subject:    "vault:arrstack:readonly",
+		Apps:       []string{"sonarr"},
+		Methods:    []string{"GET", "HEAD"},
+		TTLSeconds: 60,
+	}); err != nil {
+		t.Fatalf("MintToken: %v", err)
+	}
+	if strings.Join(m.lastRequest.Methods, ",") != "GET,HEAD" {
+		t.Fatalf("expected methods forwarded, got %v", m.lastRequest.Methods)
+	}
+}
+
+func TestClient_MintToken_RejectsUnknownMethod(t *testing.T) {
+	m := newMockArrproxy(t)
+	client, _ := newClient(&arrstackConfig{BaseURL: m.server.URL, AdminToken: m.adminToken})
+
+	_, err := client.MintToken(context.Background(), mintTokenRequest{
+		Subject:    "vault:arrstack:readonly",
+		Apps:       []string{"sonarr"},
+		Methods:    []string{"FETCH"},
+		TTLSeconds: 60,
+	})
+	if err == nil {
+		t.Fatal("expected arrproxy to reject an unknown HTTP method")
+	}
+}
+
 func TestClient_MintToken_RejectsBadSubject(t *testing.T) {
 	m := newMockArrproxy(t)
 	client, _ := newClient(&arrstackConfig{BaseURL: m.server.URL, AdminToken: m.adminToken})

path_credentials.go

@@ -75,6 +75,7 @@ func (b *arrstackBackend) mintToken(ctx context.Context, req *logical.Request, r
 	minted, err := client.MintToken(ctx, mintTokenRequest{
 		Subject:    subject,
 		Apps:       role.Apps,
+		Methods:    role.Methods,
 		Label:      label,
 		TTLSeconds: int64(ttl.Seconds()),
 	})
@@ -98,6 +99,7 @@ func (b *arrstackBackend) mintToken(ctx context.Context, req *logical.Request, r
 		"token":      minted.Token,
 		"id":         minted.ID,
 		"apps":       role.Apps,
+		"methods":    role.Methods,
 		"subject":    subject,
 		"expires_at": expiresAt.Format(time.RFC3339),
 	}

path_credentials_test.go

@@ -93,6 +93,63 @@ func TestCredentials_MintAndRevoke(t *testing.T) {
 	}
 }
 
+func TestCredentials_MethodsForwardedAndEchoed(t *testing.T) {
+	b, s := getTestBackend(t)
+	m := newMockArrproxy(t)
+	writeTestConfig(t, b, s, m.server.URL, m.adminToken)
+	createRole(t, b, s, "readonly", map[string]interface{}{
+		"apps":    "sonarr",
+		"methods": "head,get",
+		"ttl":     "1h",
+	})
+
+	resp, err := b.HandleRequest(context.Background(), &logical.Request{
+		Operation: logical.ReadOperation,
+		Path:      "creds/readonly",
+		Storage:   s,
+	})
+	if err != nil || resp == nil {
+		t.Fatalf("mint creds: err=%v resp=%v", err, resp)
+	}
+
+	// The role's normalized method scope reached arrproxy.
+	if strings.Join(m.lastRequest.Methods, ",") != "GET,HEAD" {
+		t.Fatalf("expected methods GET,HEAD forwarded, got %v", m.lastRequest.Methods)
+	}
+	// And is echoed back to the caller alongside apps/subject.
+	if strings.Join(resp.Data["methods"].([]string), ",") != "GET,HEAD" {
+		t.Fatalf("expected methods echoed in creds response, got %v", resp.Data["methods"])
+	}
+}
+
+func TestCredentials_NoMethodsOmitsTheField(t *testing.T) {
+	b, s := getTestBackend(t)
+	m := newMockArrproxy(t)
+	writeTestConfig(t, b, s, m.server.URL, m.adminToken)
+	createRole(t, b, s, "media", map[string]interface{}{"apps": "sonarr", "ttl": "1h"})
+
+	resp, err := b.HandleRequest(context.Background(), &logical.Request{
+		Operation: logical.ReadOperation,
+		Path:      "creds/media",
+		Storage:   s,
+	})
+	if err != nil || resp == nil {
+		t.Fatalf("mint creds: err=%v resp=%v", err, resp)
+	}
+
+	// An unscoped role sends no methods key at all, so an arrproxy predating
+	// method scoping sees the request exactly as before.
+	if strings.Contains(string(m.lastBody), "methods") {
+		t.Fatalf("expected methods omitted from the mint body, got %s", m.lastBody)
+	}
+	if len(m.lastRequest.Methods) != 0 {
+		t.Fatalf("expected no methods forwarded, got %v", m.lastRequest.Methods)
+	}
+	if methods, ok := resp.Data["methods"].([]string); ok && len(methods) != 0 {
+		t.Fatalf("expected an empty method scope in the response, got %v", methods)
+	}
+}
+
 func TestCredentials_UnknownRole(t *testing.T) {
 	b, s := getTestBackend(t)
 	m := newMockArrproxy(t)

path_roles.go

@@ -3,7 +3,9 @@ package arrstack
 import (
 	"context"
 	"fmt"
+	"net/http"
 	"sort"
+	"strings"
 	"time"
 
 	"github.com/hashicorp/vault/sdk/framework"
@@ -20,10 +22,21 @@ var knownApps = map[string]bool{
 	"prowlarr": true,
 }
 
+// knownMethods mirrors arrproxy's accepted HTTP method scope. Validating here
+// rejects a typo at role write instead of at mint.
+var knownMethods = map[string]bool{
+	http.MethodGet: true, http.MethodHead: true, http.MethodPost: true,
+	http.MethodPut: true, http.MethodPatch: true, http.MethodDelete: true,
+	http.MethodOptions: true,
+}
+
 // arrstackRole constrains the machine tokens minted from the creds/<name> path.
 type arrstackRole struct {
 	// Apps is the subset of sonarr/radarr/prowlarr a minted token may reach.
 	Apps []string `json:"apps"`
+	// Methods, when non-empty, limits a minted token to those HTTP methods.
+	// Empty means unrestricted.
+	Methods []string `json:"methods,omitempty"`
 	// TTL is the default lease duration for tokens issued from this role.
 	TTL time.Duration `json:"ttl"`
 	// MaxTTL is the maximum lease duration for tokens issued from this role.
@@ -33,6 +46,7 @@ type arrstackRole struct {
 func (r *arrstackRole) toResponseData() map[string]interface{} {
 	return map[string]interface{}{
 		"apps":    r.Apps,
+		"methods": r.Methods,
 		"ttl":     int64(r.TTL.Seconds()),
 		"max_ttl": int64(r.MaxTTL.Seconds()),
 	}
@@ -59,6 +73,28 @@ func validateApps(requested []string) ([]string, error) {
 	return out, nil
 }
 
+// validateMethods uppercase-normalizes, de-duplicates and sorts a requested
+// method scope. An empty request yields a nil scope, meaning unrestricted.
+func validateMethods(requested []string) ([]string, error) {
+	if len(requested) == 0 {
+		return nil, nil
+	}
+	seen := map[string]bool{}
+	out := make([]string, 0, len(requested))
+	for _, m := range requested {
+		m = strings.ToUpper(strings.TrimSpace(m))
+		if !knownMethods[m] {
+			return nil, fmt.Errorf("unknown method %q: methods must be a subset of GET/HEAD/POST/PUT/PATCH/DELETE/OPTIONS", m)
+		}
+		if !seen[m] {
+			seen[m] = true
+			out = append(out, m)
+		}
+	}
+	sort.Strings(out)
+	return out, nil
+}
+
 func pathRole(b *arrstackBackend) *framework.Path {
 	return &framework.Path{
 		Pattern: "roles/" + framework.GenericNameRegex("name"),
@@ -77,6 +113,10 @@ func pathRole(b *arrstackBackend) *framework.Path {
 				Description: "Comma-separated subset of sonarr/radarr/prowlarr a minted token may reach.",
 				Required:    true,
 			},
+			"methods": {
+				Type:        framework.TypeCommaStringSlice,
+				Description: "Optional comma-separated HTTP methods a minted token is limited to (GET/HEAD/POST/PUT/PATCH/DELETE/OPTIONS). Empty means unrestricted.",
+			},
 			"ttl": {
 				Type:        framework.TypeDurationSecond,
 				Description: "Default lease TTL for tokens minted from this role.",
@@ -171,6 +211,13 @@ func (b *arrstackBackend) pathRoleWrite(ctx context.Context, req *logical.Reques
 		}
 		role.Apps = apps
 	}
+	if v, ok := data.GetOk("methods"); ok {
+		methods, err := validateMethods(v.([]string))
+		if err != nil {
+			return logical.ErrorResponse(err.Error()), nil
+		}
+		role.Methods = methods
+	}
 	if v, ok := data.GetOk("ttl"); ok {
 		role.TTL = time.Duration(v.(int)) * time.Second
 	}

path_roles_test.go

@@ -2,6 +2,7 @@ package arrstack
 
 import (
 	"context"
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/vault/sdk/logical"
@@ -148,6 +149,134 @@ func TestRole_TTLGreaterThanMaxTTLRejected(t *testing.T) {
 	}
 }
 
+func TestRole_MethodsStoredNormalized(t *testing.T) {
+	b, s := getTestBackend(t)
+	ctx := context.Background()
+
+	resp, err := b.HandleRequest(ctx, &logical.Request{
+		Operation: logical.CreateOperation,
+		Path:      "roles/readonly",
+		Storage:   s,
+		Data: map[string]interface{}{
+			"apps":    "sonarr",
+			"methods": "get, head ,GET",
+		},
+	})
+	if err != nil || (resp != nil && resp.IsError()) {
+		t.Fatalf("write role: err=%v resp=%v", err, resp)
+	}
+
+	resp, err = b.HandleRequest(ctx, &logical.Request{
+		Operation: logical.ReadOperation,
+		Path:      "roles/readonly",
+		Storage:   s,
+	})
+	if err != nil || resp == nil {
+		t.Fatalf("read role: err=%v resp=%v", err, resp)
+	}
+	methods := resp.Data["methods"].([]string)
+	// Uppercased, de-duplicated and sorted.
+	if strings.Join(methods, ",") != "GET,HEAD" {
+		t.Fatalf("unexpected methods: %v", methods)
+	}
+}
+
+func TestRole_MethodsDefaultEmpty(t *testing.T) {
+	b, s := getTestBackend(t)
+	ctx := context.Background()
+
+	resp, err := b.HandleRequest(ctx, &logical.Request{
+		Operation: logical.CreateOperation,
+		Path:      "roles/unrestricted",
+		Storage:   s,
+		Data:      map[string]interface{}{"apps": "sonarr"},
+	})
+	if err != nil || (resp != nil && resp.IsError()) {
+		t.Fatalf("write role: err=%v resp=%v", err, resp)
+	}
+
+	role, _ := b.getRole(ctx, s, "unrestricted")
+	if len(role.Methods) != 0 {
+		t.Fatalf("expected no method scope by default, got %v", role.Methods)
+	}
+}
+
+func TestRole_UnknownMethodRejected(t *testing.T) {
+	b, s := getTestBackend(t)
+
+	resp, err := b.HandleRequest(context.Background(), &logical.Request{
+		Operation: logical.CreateOperation,
+		Path:      "roles/bad",
+		Storage:   s,
+		Data:      map[string]interface{}{"apps": "sonarr", "methods": "GET,FETCH"},
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if resp == nil || !resp.IsError() {
+		t.Fatal("expected an error for a method outside the known HTTP set")
+	}
+	role, _ := b.getRole(context.Background(), s, "bad")
+	if role != nil {
+		t.Fatal("expected the role not to be stored when methods are invalid")
+	}
+}
+
+func TestRole_MethodsClearedOnUpdate(t *testing.T) {
+	b, s := getTestBackend(t)
+	ctx := context.Background()
+
+	createRole(t, b, s, "media", map[string]interface{}{"apps": "sonarr", "methods": "GET"})
+
+	resp, err := b.HandleRequest(ctx, &logical.Request{
+		Operation: logical.UpdateOperation,
+		Path:      "roles/media",
+		Storage:   s,
+		Data:      map[string]interface{}{"methods": ""},
+	})
+	if err != nil || (resp != nil && resp.IsError()) {
+		t.Fatalf("update role: err=%v resp=%v", err, resp)
+	}
+	role, _ := b.getRole(ctx, s, "media")
+	if len(role.Methods) != 0 {
+		t.Fatalf("expected methods cleared, got %v", role.Methods)
+	}
+	if len(role.Apps) != 1 {
+		t.Fatalf("expected apps preserved across the update, got %v", role.Apps)
+	}
+}
+
+func TestValidateMethods(t *testing.T) {
+	cases := []struct {
+		name    string
+		in      []string
+		want    []string
+		wantErr bool
+	}{
+		{"empty is unrestricted", nil, nil, false},
+		{"lowercase normalized", []string{"get"}, []string{"GET"}, false},
+		{"trimmed dedup and sort", []string{" head ", "GET", "head"}, []string{"GET", "HEAD"}, false},
+		{"all known", []string{"OPTIONS", "DELETE", "PATCH", "PUT", "POST", "HEAD", "GET"},
+			[]string{"DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"}, false},
+		{"unknown", []string{"GET", "FETCH"}, nil, true},
+		{"empty entry", []string{""}, nil, true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got, err := validateMethods(tc.in)
+			if (err != nil) != tc.wantErr {
+				t.Fatalf("validateMethods err=%v wantErr=%v", err, tc.wantErr)
+			}
+			if tc.wantErr {
+				return
+			}
+			if strings.Join(got, ",") != strings.Join(tc.want, ",") {
+				t.Fatalf("got %v want %v", got, tc.want)
+			}
+		})
+	}
+}
+
 func TestValidateApps(t *testing.T) {
 	cases := []struct {
 		name    string