Add AI service API token auth

internal/httpapi/auth.go

@@ -0,0 +1,30 @@
+package httpapi
+
+import (
+	"crypto/subtle"
+	"net/http"
+	"strings"
+)
+
+func (s *Server) requireAPIToken(path string, r *http.Request) bool {
+	if !strings.HasPrefix(path, "/api/v1/") && path != "/api/v1" {
+		return true
+	}
+	expected := strings.TrimSpace(s.cfg.APIAuthToken)
+	if expected == "" {
+		return true
+	}
+	got := bearerToken(r.Header.Get("Authorization"))
+	if got == "" {
+		return false
+	}
+	return subtle.ConstantTimeCompare([]byte(got), []byte(expected)) == 1
+}
+
+func bearerToken(header string) string {
+	header = strings.TrimSpace(header)
+	if len(header) < len("Bearer ") || !strings.EqualFold(header[:len("Bearer ")], "Bearer ") {
+		return ""
+	}
+	return strings.TrimSpace(header[len("Bearer "):])
+}

internal/httpapi/auth_test.go

@@ -0,0 +1,47 @@
+package httpapi
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"ai-service/internal/config"
+)
+
+func TestAPITokenProtectsAPIRoutes(t *testing.T) {
+	srv := NewServer(nil, config.Config{APIAuthToken: "secret"})
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/stats", nil)
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("expected unauthorized API request to be 401, got %d", rec.Code)
+	}
+
+	req = httptest.NewRequest(http.MethodGet, "/api/v1/not-found", nil)
+	req.Header.Set("Authorization", "Bearer wrong")
+	rec = httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("expected wrong token to be 401, got %d", rec.Code)
+	}
+
+	req = httptest.NewRequest(http.MethodGet, "/api/v1/not-found", nil)
+	req.Header.Set("Authorization", "Bearer secret")
+	rec = httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("expected authorized unknown route to be 404, got %d", rec.Code)
+	}
+}
+
+func TestAPITokenDoesNotProtectHealth(t *testing.T) {
+	srv := NewServer(nil, config.Config{APIAuthToken: "secret"})
+
+	req := httptest.NewRequest(http.MethodGet, "/healthz", nil)
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("expected healthz to stay open, got %d", rec.Code)
+	}
+}

internal/httpapi/server.go

@@ -29,6 +29,10 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if path == "" {
 		path = "/"
 	}
+	if !s.requireAPIToken(path, r) {
+		writeError(w, http.StatusUnauthorized, "unauthorized")
+		return
+	}
 	switch {
 	case r.Method == http.MethodGet && path == "/healthz":
 		writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})