feat: add JWT authentication middleware

.mcp.json

@@ -0,0 +1,9 @@
+{
+  "mcpServers": {
+    "devharness": {
+      "command": "/Users/baai/codebase/DevHarness/devharness",
+      "args": ["serve"],
+      "env": {}
+    }
+  }
+}

main.go

@@ -6,6 +6,7 @@ import (
 	"os"
 
 	"github.com/wbavon/devharness-testbed/handlers"
+	"github.com/wbavon/devharness-testbed/middleware"
 )
 
 func main() {
@@ -18,13 +19,21 @@ func main() {
 	mux.HandleFunc("PUT /api/items/{id}", handlers.UpdateItem)
 	mux.HandleFunc("DELETE /api/items/{id}", handlers.DeleteItem)
 
+	jwtSecret := os.Getenv("JWT_SECRET")
+	if jwtSecret == "" {
+		log.Fatal("JWT_SECRET environment variable is required")
+	}
+
+	authMiddleware := middleware.Auth(jwtSecret, []string{"/health"})
+	handler := authMiddleware(mux)
+
 	port := os.Getenv("PORT")
 	if port == "" {
 		port = "8080"
 	}
 
 	log.Printf("Starting server on :%s", port)
-	if err := http.ListenAndServe(":"+port, mux); err != nil {
+	if err := http.ListenAndServe(":"+port, handler); err != nil {
 		log.Fatalf("Server failed: %v", err)
 	}
 }

middleware/auth.go

@@ -0,0 +1,121 @@
+package middleware
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// Auth returns middleware that validates JWT Bearer tokens from the
+// Authorization header. Requests to paths listed in skipPaths bypass
+// authentication. The token is validated using the provided secret with
+// HMAC-SHA256 (HS256).
+func Auth(secret string, skipPaths []string) func(http.Handler) http.Handler {
+	skip := make(map[string]bool, len(skipPaths))
+	for _, p := range skipPaths {
+		skip[p] = true
+	}
+
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if skip[r.URL.Path] {
+				next.ServeHTTP(w, r)
+				return
+			}
+
+			authHeader := r.Header.Get("Authorization")
+			if authHeader == "" {
+				http.Error(w, `{"error":"missing authorization header"}`, http.StatusUnauthorized)
+				return
+			}
+
+			parts := strings.SplitN(authHeader, " ", 2)
+			if len(parts) != 2 || !strings.EqualFold(parts[0], "Bearer") {
+				http.Error(w, `{"error":"invalid authorization header format"}`, http.StatusUnauthorized)
+				return
+			}
+
+			token := parts[1]
+			if err := validateJWT(token, secret); err != nil {
+				http.Error(w, `{"error":"invalid token"}`, http.StatusUnauthorized)
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
+// jwtHeader is the expected header for HS256 tokens.
+type jwtHeader struct {
+	Alg string `json:"alg"`
+	Typ string `json:"typ"`
+}
+
+// jwtPayload contains the standard claims we validate.
+type jwtPayload struct {
+	Exp int64  `json:"exp,omitempty"`
+	Sub string `json:"sub,omitempty"`
+}
+
+func validateJWT(token, secret string) error {
+	segments := strings.SplitN(token, ".", 3)
+	if len(segments) != 3 {
+		return errInvalidToken
+	}
+
+	// Verify header
+	headerBytes, err := base64.RawURLEncoding.DecodeString(segments[0])
+	if err != nil {
+		return errInvalidToken
+	}
+	var h jwtHeader
+	if err := json.Unmarshal(headerBytes, &h); err != nil {
+		return errInvalidToken
+	}
+	if h.Alg != "HS256" {
+		return errInvalidToken
+	}
+
+	// Verify signature
+	signingInput := segments[0] + "." + segments[1]
+	mac := hmac.New(sha256.New, []byte(secret))
+	mac.Write([]byte(signingInput))
+	expectedSig := mac.Sum(nil)
+
+	actualSig, err := base64.RawURLEncoding.DecodeString(segments[2])
+	if err != nil {
+		return errInvalidToken
+	}
+	if !hmac.Equal(expectedSig, actualSig) {
+		return errInvalidToken
+	}
+
+	// Check expiry
+	payloadBytes, err := base64.RawURLEncoding.DecodeString(segments[1])
+	if err != nil {
+		return errInvalidToken
+	}
+	var p jwtPayload
+	if err := json.Unmarshal(payloadBytes, &p); err != nil {
+		return errInvalidToken
+	}
+	if p.Exp > 0 && time.Now().Unix() > p.Exp {
+		return errTokenExpired
+	}
+
+	return nil
+}
+
+type tokenError string
+
+func (e tokenError) Error() string { return string(e) }
+
+const (
+	errInvalidToken tokenError = "invalid token"
+	errTokenExpired tokenError = "token expired"
+)

middleware/auth_test.go

@@ -0,0 +1,155 @@
+package middleware
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+// buildJWT creates a signed HS256 JWT for testing purposes.
+func buildJWT(header, payload map[string]any, secret string) string {
+	h, _ := json.Marshal(header)
+	p, _ := json.Marshal(payload)
+
+	seg0 := base64.RawURLEncoding.EncodeToString(h)
+	seg1 := base64.RawURLEncoding.EncodeToString(p)
+
+	signingInput := seg0 + "." + seg1
+	mac := hmac.New(sha256.New, []byte(secret))
+	mac.Write([]byte(signingInput))
+	sig := base64.RawURLEncoding.EncodeToString(mac.Sum(nil))
+
+	return seg0 + "." + seg1 + "." + sig
+}
+
+func validToken(secret string) string {
+	return buildJWT(
+		map[string]any{"alg": "HS256", "typ": "JWT"},
+		map[string]any{"sub": "user1", "exp": time.Now().Add(time.Hour).Unix()},
+		secret,
+	)
+}
+
+func expiredToken(secret string) string {
+	return buildJWT(
+		map[string]any{"alg": "HS256", "typ": "JWT"},
+		map[string]any{"sub": "user1", "exp": time.Now().Add(-time.Hour).Unix()},
+		secret,
+	)
+}
+
+var okHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(http.StatusOK)
+	w.Write([]byte("ok"))
+})
+
+const testSecret = "test-secret-key"
+
+func TestAuth_ValidToken(t *testing.T) {
+	mw := Auth(testSecret, nil)
+	handler := mw(okHandler)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
+	req.Header.Set("Authorization", "Bearer "+validToken(testSecret))
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", w.Code)
+	}
+}
+
+func TestAuth_MissingHeader(t *testing.T) {
+	mw := Auth(testSecret, nil)
+	handler := mw(okHandler)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", w.Code)
+	}
+}
+
+func TestAuth_InvalidFormat(t *testing.T) {
+	mw := Auth(testSecret, nil)
+	handler := mw(okHandler)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
+	req.Header.Set("Authorization", "Basic abc123")
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", w.Code)
+	}
+}
+
+func TestAuth_InvalidSignature(t *testing.T) {
+	mw := Auth(testSecret, nil)
+	handler := mw(okHandler)
+
+	token := validToken("wrong-secret")
+	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
+	req.Header.Set("Authorization", "Bearer "+token)
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", w.Code)
+	}
+}
+
+func TestAuth_ExpiredToken(t *testing.T) {
+	mw := Auth(testSecret, nil)
+	handler := mw(okHandler)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
+	req.Header.Set("Authorization", "Bearer "+expiredToken(testSecret))
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", w.Code)
+	}
+}
+
+func TestAuth_SkipPaths(t *testing.T) {
+	mw := Auth(testSecret, []string{"/health"})
+	handler := mw(okHandler)
+
+	req := httptest.NewRequest(http.MethodGet, "/health", nil)
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected 200 for skipped path, got %d", w.Code)
+	}
+}
+
+func TestAuth_MalformedToken(t *testing.T) {
+	mw := Auth(testSecret, nil)
+	handler := mw(okHandler)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
+	req.Header.Set("Authorization", "Bearer not.a.valid.jwt")
+	w := httptest.NewRecorder()
+
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", w.Code)
+	}
+}