feat(auth): add Dex JWT middleware to supervisor, routing pod, and brain MCP

Closes #6 on gitea.d-ma.be/mathias/hyperguild.

Dex is deployed at auth.d-ma.be. All three MCP servers now accept JWTs
issued by Dex in addition to static bearer tokens, enabling claude.ai
OAuth 2.0 integration without abandoning backward-compat CLI auth.

Changes:
- internal/auth/: new Validator (JWKS auto-refresh via lestrrat-go/jwx/v2),
  ProtectedResourceHandler (RFC 9728 /.well-known/oauth-protected-resource)
- internal/mcp/Server: adds optional *auth.Validator; checkAuth tries JWT
  first, then static token fallback; both-nil = auth disabled (unchanged default)
- cmd/supervisor, cmd/routing: construct Validator from DEX_ISSUER_URL +
  MCP_AUDIENCE env vars; register protected-resource handler when set
- ingestion/internal/auth/: same Validator + handler (separate module)
- ingestion/internal/mcp/BearerAuth: same JWT-or-static chain
- ingestion/cmd/server: same wiring pattern

New env vars (all optional; absent = static-token-only, same as before):
  DEX_ISSUER_URL   — Dex issuer URL (e.g. https://auth.d-ma.be)
  MCP_AUDIENCE     — expected aud claim (e.g. brain, supervisor)
  MCP_RESOURCE_URL — resource identifier for RFC 9728 metadata response

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/auth/jwt.go

@@ -0,0 +1,84 @@
+package auth
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/lestrrat-go/jwx/v2/jwk"
+	"github.com/lestrrat-go/jwx/v2/jwt"
+)
+
+// Validator validates Bearer JWTs issued by a Dex (OIDC) authorization server.
+// Audience is optional; leave empty to skip audience validation.
+type Validator struct {
+	issuer   string
+	audience string
+	jwksURI  string
+	cache    *jwk.Cache
+}
+
+// NewValidator fetches the OIDC discovery document from issuerURL, extracts
+// jwks_uri, seeds the JWKS cache, and returns a ready Validator.
+// If DEX_ISSUER_URL is not set the caller should pass "" and skip construction.
+func NewValidator(issuerURL, audience string) (*Validator, error) {
+	resp, err := http.Get(issuerURL + "/.well-known/openid-configuration") //nolint:noctx
+	if err != nil {
+		return nil, fmt.Errorf("fetch oidc discovery: %w", err)
+	}
+	defer resp.Body.Close() //nolint:errcheck
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("oidc discovery: status %d", resp.StatusCode)
+	}
+
+	var doc struct {
+		JWKSURI string `json:"jwks_uri"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&doc); err != nil {
+		return nil, fmt.Errorf("decode oidc discovery: %w", err)
+	}
+	if doc.JWKSURI == "" {
+		return nil, fmt.Errorf("oidc discovery: empty jwks_uri")
+	}
+
+	ctx := context.Background()
+	cache := jwk.NewCache(ctx)
+	if err := cache.Register(doc.JWKSURI, jwk.WithMinRefreshInterval(time.Hour)); err != nil {
+		return nil, fmt.Errorf("register jwks cache: %w", err)
+	}
+	if _, err := cache.Refresh(ctx, doc.JWKSURI); err != nil {
+		return nil, fmt.Errorf("initial jwks fetch: %w", err)
+	}
+
+	return &Validator{
+		issuer:   issuerURL,
+		audience: audience,
+		jwksURI:  doc.JWKSURI,
+		cache:    cache,
+	}, nil
+}
+
+// Validate parses and validates rawToken. Returns the subject claim on success.
+func (v *Validator) Validate(ctx context.Context, rawToken string) (string, error) {
+	keySet, err := v.cache.Get(ctx, v.jwksURI)
+	if err != nil {
+		return "", fmt.Errorf("get jwks: %w", err)
+	}
+
+	opts := []jwt.ParseOption{
+		jwt.WithKeySet(keySet),
+		jwt.WithValidate(true),
+		jwt.WithIssuer(v.issuer),
+	}
+	if v.audience != "" {
+		opts = append(opts, jwt.WithAudience(v.audience))
+	}
+
+	tok, err := jwt.ParseString(rawToken, opts...)
+	if err != nil {
+		return "", fmt.Errorf("validate jwt: %w", err)
+	}
+	return tok.Subject(), nil
+}

internal/auth/jwt_test.go

@@ -0,0 +1,169 @@
+package auth_test
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/rsa"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/lestrrat-go/jwx/v2/jwa"
+	"github.com/lestrrat-go/jwx/v2/jwk"
+	"github.com/lestrrat-go/jwx/v2/jwt"
+	"github.com/mathiasbq/supervisor/internal/auth"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type testKeys struct {
+	priv jwk.Key
+	pub  jwk.Key
+}
+
+func generateRSAKeys(t *testing.T) testKeys {
+	t.Helper()
+	raw, err := rsa.GenerateKey(rand.Reader, 2048)
+	require.NoError(t, err)
+
+	priv, err := jwk.FromRaw(raw)
+	require.NoError(t, err)
+	require.NoError(t, priv.Set(jwk.KeyIDKey, "test-kid"))
+	require.NoError(t, priv.Set(jwk.AlgorithmKey, jwa.RS256))
+
+	pub, err := jwk.PublicKeyOf(priv)
+	require.NoError(t, err)
+
+	return testKeys{priv: priv, pub: pub}
+}
+
+func mockOIDCServer(t *testing.T, keys testKeys) *httptest.Server {
+	t.Helper()
+	set := jwk.NewSet()
+	require.NoError(t, set.AddKey(keys.pub))
+	jwksBytes, err := json.Marshal(set)
+	require.NoError(t, err)
+
+	mux := http.NewServeMux()
+	var srv *httptest.Server
+	mux.HandleFunc("/.well-known/openid-configuration", func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]string{
+			"issuer":   srv.URL,
+			"jwks_uri": srv.URL + "/jwks",
+		})
+	})
+	mux.HandleFunc("/jwks", func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write(jwksBytes)
+	})
+	srv = httptest.NewServer(mux)
+	t.Cleanup(srv.Close)
+	return srv
+}
+
+func signToken(t *testing.T, keys testKeys, issuer, audience, subject string, exp time.Time) string {
+	t.Helper()
+	b := jwt.NewBuilder().
+		Issuer(issuer).
+		Subject(subject).
+		Expiration(exp)
+	if audience != "" {
+		b = b.Audience([]string{audience})
+	}
+	tok, err := b.Build()
+	require.NoError(t, err)
+	signed, err := jwt.Sign(tok, jwt.WithKey(jwa.RS256, keys.priv))
+	require.NoError(t, err)
+	return string(signed)
+}
+
+func TestValidator(t *testing.T) {
+	keys := generateRSAKeys(t)
+	srv := mockOIDCServer(t, keys)
+	ctx := context.Background()
+
+	v, err := auth.NewValidator(srv.URL, "brain")
+	require.NoError(t, err)
+
+	tests := []struct {
+		name      string
+		token     string
+		wantSub   string
+		wantErr   bool
+	}{
+		{
+			name:    "valid jwt",
+			token:   signToken(t, keys, srv.URL, "brain", "test-user", time.Now().Add(time.Hour)),
+			wantSub: "test-user",
+		},
+		{
+			name:    "expired jwt",
+			token:   signToken(t, keys, srv.URL, "brain", "test-user", time.Now().Add(-time.Hour)),
+			wantErr: true,
+		},
+		{
+			name:    "wrong issuer",
+			token:   signToken(t, keys, "https://evil.example.com", "brain", "test-user", time.Now().Add(time.Hour)),
+			wantErr: true,
+		},
+		{
+			name:    "wrong audience",
+			token:   signToken(t, keys, srv.URL, "other-service", "test-user", time.Now().Add(time.Hour)),
+			wantErr: true,
+		},
+		{
+			name:    "tampered token",
+			token:   signToken(t, keys, srv.URL, "brain", "test-user", time.Now().Add(time.Hour)) + "tampered",
+			wantErr: true,
+		},
+		{
+			name:    "not a jwt",
+			token:   "not-a-jwt",
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			sub, err := v.Validate(ctx, tc.token)
+			if tc.wantErr {
+				assert.Error(t, err)
+				assert.Empty(t, sub)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, tc.wantSub, sub)
+			}
+		})
+	}
+}
+
+func TestNewValidator_NoAudience(t *testing.T) {
+	keys := generateRSAKeys(t)
+	srv := mockOIDCServer(t, keys)
+	ctx := context.Background()
+
+	v, err := auth.NewValidator(srv.URL, "")
+	require.NoError(t, err)
+
+	// Token without audience passes when audience validation is disabled.
+	tok, err := jwt.NewBuilder().
+		Issuer(srv.URL).
+		Subject("sub").
+		Expiration(time.Now().Add(time.Hour)).
+		Build()
+	require.NoError(t, err)
+	signed, err := jwt.Sign(tok, jwt.WithKey(jwa.RS256, keys.priv))
+	require.NoError(t, err)
+
+	sub, err := v.Validate(ctx, string(signed))
+	require.NoError(t, err)
+	assert.Equal(t, "sub", sub)
+}
+
+func TestNewValidator_BadDiscoveryURL(t *testing.T) {
+	_, err := auth.NewValidator("http://127.0.0.1:1", "brain")
+	assert.Error(t, err)
+}

internal/auth/protected_resource.go

@@ -0,0 +1,23 @@
+package auth
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// ProtectedResourceHandler returns an RFC 9728 oauth-protected-resource metadata
+// handler. Mount at GET /.well-known/oauth-protected-resource (no auth required).
+func ProtectedResourceHandler(resourceURL, issuerURL string) http.HandlerFunc {
+	type metadata struct {
+		Resource             string   `json:"resource"`
+		AuthorizationServers []string `json:"authorization_servers"`
+	}
+	body, _ := json.Marshal(metadata{
+		Resource:             resourceURL,
+		AuthorizationServers: []string{issuerURL},
+	})
+	return func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write(body)
+	}
+}

internal/auth/protected_resource_test.go

@@ -0,0 +1,28 @@
+package auth_test
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/mathiasbq/supervisor/internal/auth"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestProtectedResourceHandler(t *testing.T) {
+	h := auth.ProtectedResourceHandler("https://brain-mcp.d-ma.be", "https://auth.d-ma.be")
+	req := httptest.NewRequest(http.MethodGet, "/.well-known/oauth-protected-resource", nil)
+	rr := httptest.NewRecorder()
+	h(rr, req)
+
+	assert.Equal(t, http.StatusOK, rr.Code)
+	assert.Equal(t, "application/json", rr.Header().Get("Content-Type"))
+
+	var body map[string]any
+	require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &body))
+	assert.Equal(t, "https://brain-mcp.d-ma.be", body["resource"])
+	servers := body["authorization_servers"].([]any)
+	assert.Equal(t, "https://auth.d-ma.be", servers[0])
+}

internal/mcp/server.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/mathiasbq/supervisor/internal/auth"
 	"github.com/mathiasbq/supervisor/internal/registry"
 )
 
@@ -32,15 +33,16 @@ type rpcError struct {
 
 // Server is an HTTP handler implementing the MCP JSON-RPC protocol.
 type Server struct {
-	reg   *registry.Registry
-	token string
+	reg       *registry.Registry
+	token     string
+	validator *auth.Validator
 }
 
-// NewServer constructs an MCP HTTP handler. If token is non-empty, every
-// request must carry "Authorization: Bearer <token>" or it is rejected with
-// HTTP 401 and JSON-RPC error -32001. Empty token disables auth (default).
-func NewServer(reg *registry.Registry, token string) *Server {
-	return &Server{reg: reg, token: token}
+// NewServer constructs an MCP HTTP handler. token is the static bearer token
+// (empty disables static auth). validator is optional; when non-nil, a valid
+// JWT from Dex is accepted in addition to the static token.
+func NewServer(reg *registry.Registry, token string, validator *auth.Validator) *Server {
+	return &Server{reg: reg, token: token, validator: validator}
 }
 
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -120,27 +122,42 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
-// checkAuth verifies the bearer token when one is configured. Returns true if
-// the request may proceed, false if it has been rejected (401 already written).
+// checkAuth verifies the bearer token. Accepts a valid Dex JWT (when validator
+// is configured) or the static token. Returns true if the request may proceed.
+// When neither token nor validator is configured, auth is disabled (default).
 func (s *Server) checkAuth(w http.ResponseWriter, r *http.Request) bool {
-	if s.token == "" {
+	if s.token == "" && s.validator == nil {
 		return true
 	}
 
-	const prefix = "Bearer "
-	hdr := r.Header.Get("Authorization")
-	if !strings.HasPrefix(hdr, prefix) ||
-		subtle.ConstantTimeCompare([]byte(hdr[len(prefix):]), []byte(s.token)) != 1 {
-		slog.Warn("mcp auth rejected", "remote", r.RemoteAddr, "method", r.Method)
-		w.Header().Set("Content-Type", "application/json")
-		w.WriteHeader(http.StatusUnauthorized)
-		_ = json.NewEncoder(w).Encode(response{
-			JSONRPC: "2.0",
-			Error:   &rpcError{Code: -32001, Message: "unauthorized"},
-		})
+	rawToken, ok := strings.CutPrefix(r.Header.Get("Authorization"), "Bearer ")
+	if !ok {
+		s.rejectAuth(w, r)
 		return false
 	}
-	return true
+
+	if s.validator != nil {
+		if _, err := s.validator.Validate(r.Context(), rawToken); err == nil {
+			return true
+		}
+	}
+
+	if s.token != "" && subtle.ConstantTimeCompare([]byte(rawToken), []byte(s.token)) == 1 {
+		return true
+	}
+
+	s.rejectAuth(w, r)
+	return false
+}
+
+func (s *Server) rejectAuth(w http.ResponseWriter, r *http.Request) {
+	slog.Warn("mcp auth rejected", "remote", r.RemoteAddr, "method", r.Method)
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusUnauthorized)
+	_ = json.NewEncoder(w).Encode(response{
+		JSONRPC: "2.0",
+		Error:   &rpcError{Code: -32001, Message: "unauthorized"},
+	})
 }
 
 func writeError(w http.ResponseWriter, id any, code int, msg string) {

internal/mcp/server_test.go

@@ -23,7 +23,7 @@ func jsonBody(t *testing.T, v any) *bytes.Buffer {
 
 func TestMCPInitialize(t *testing.T) {
 	reg := registry.New()
-	srv := mcp.NewServer(reg, "")
+	srv := mcp.NewServer(reg, "", nil)
 
 	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
 		"jsonrpc": "2.0",
@@ -45,7 +45,7 @@ func TestMCPInitialize(t *testing.T) {
 
 func TestMCPToolsList(t *testing.T) {
 	reg := registry.New()
-	srv := mcp.NewServer(reg, "")
+	srv := mcp.NewServer(reg, "", nil)
 
 	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
 		"jsonrpc": "2.0", "id": 2, "method": "tools/list", "params": map[string]any{},
@@ -63,7 +63,7 @@ func TestMCPToolsList(t *testing.T) {
 
 func TestMCPUnknownMethod(t *testing.T) {
 	reg := registry.New()
-	srv := mcp.NewServer(reg, "")
+	srv := mcp.NewServer(reg, "", nil)
 
 	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
 		"jsonrpc": "2.0", "id": 3, "method": "unknown/method", "params": map[string]any{},
@@ -80,7 +80,7 @@ func TestMCPUnknownMethod(t *testing.T) {
 
 func TestMCPNotificationKnownMethodGetsNoResponseBody(t *testing.T) {
 	reg := registry.New()
-	srv := mcp.NewServer(reg, "")
+	srv := mcp.NewServer(reg, "", nil)
 
 	// JSON-RPC 2.0 notification: "id" field absent. Per spec, server MUST NOT
 	// reply. notifications/initialized is part of the standard MCP handshake.
@@ -116,7 +116,7 @@ func TestMCPAuth(t *testing.T) {
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
 			reg := registry.New()
-			srv := mcp.NewServer(reg, tc.token)
+			srv := mcp.NewServer(reg, tc.token, nil)
 
 			req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
 				"jsonrpc": "2.0", "id": 1, "method": "initialize", "params": map[string]any{},
@@ -142,7 +142,7 @@ func TestMCPAuth(t *testing.T) {
 
 func TestMCPNotificationUnknownMethodGetsNoResponseBody(t *testing.T) {
 	reg := registry.New()
-	srv := mcp.NewServer(reg, "")
+	srv := mcp.NewServer(reg, "", nil)
 
 	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
 		"jsonrpc": "2.0",