feat(security): add JWT startup guard, configurable CORS, and externalize DB credentials

- Add check_jwt_secret() that refuses default JWT secret when APP_ENV != development
- Make CORS origins configurable via CORS_ORIGINS env var (comma-separated)
- Replace hardcoded postgres credentials in docker-compose.yml with env var references
- Add APP_ENV and cors_origins to config.py
- Update .env.example with all required variables and documentation
- Add tests for JWT startup guard and CORS configuration

Closes leeworks-agents/SPARC#4
Closes leeworks-agents/SPARC#5
Closes leeworks-agents/SPARC#6

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_security.py

@@ -0,0 +1,116 @@
+"""Tests for security hardening: JWT secret startup check, CORS config, credential handling."""
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+
+class TestJWTSecretStartupCheck:
+    """Test the startup guard that refuses default JWT secret in non-dev environments."""
+
+    def test_default_secret_in_production_raises(self):
+        """Starting with default secret and APP_ENV=production must raise RuntimeError."""
+        with patch.dict(os.environ, {"APP_ENV": "production"}):
+            # Reload config to pick up the new APP_ENV
+            import importlib
+            import SPARC.config
+            importlib.reload(SPARC.config)
+
+            from SPARC.auth import _DEFAULT_JWT_SECRET, check_jwt_secret
+            # Patch JWT_SECRET to the default
+            with patch("SPARC.auth.JWT_SECRET", _DEFAULT_JWT_SECRET):
+                with pytest.raises(RuntimeError, match="FATAL.*JWT_SECRET"):
+                    check_jwt_secret()
+
+            # Restore config
+            with patch.dict(os.environ, {"APP_ENV": "development"}):
+                importlib.reload(SPARC.config)
+
+    def test_default_secret_in_development_succeeds(self):
+        """Starting with default secret and APP_ENV=development must not raise."""
+        with patch.dict(os.environ, {"APP_ENV": "development"}):
+            import importlib
+            import SPARC.config
+            importlib.reload(SPARC.config)
+
+            from SPARC.auth import _DEFAULT_JWT_SECRET, check_jwt_secret
+            with patch("SPARC.auth.JWT_SECRET", _DEFAULT_JWT_SECRET):
+                # Should not raise
+                check_jwt_secret()
+
+            # Restore
+            importlib.reload(SPARC.config)
+
+    def test_custom_secret_in_production_succeeds(self):
+        """Starting with a custom secret in production must not raise."""
+        with patch.dict(os.environ, {"APP_ENV": "production"}):
+            import importlib
+            import SPARC.config
+            importlib.reload(SPARC.config)
+
+            from SPARC.auth import check_jwt_secret
+            with patch("SPARC.auth.JWT_SECRET", "my-secure-random-secret-abc123"):
+                # Should not raise
+                check_jwt_secret()
+
+            with patch.dict(os.environ, {"APP_ENV": "development"}):
+                importlib.reload(SPARC.config)
+
+    def test_default_secret_unset_env_succeeds(self):
+        """When APP_ENV is unset (defaults to development), default secret is allowed."""
+        with patch.dict(os.environ, {}, clear=False):
+            # Remove APP_ENV if present
+            env = os.environ.copy()
+            env.pop("APP_ENV", None)
+            with patch.dict(os.environ, env, clear=True):
+                import importlib
+                import SPARC.config
+                importlib.reload(SPARC.config)
+
+                from SPARC.auth import _DEFAULT_JWT_SECRET, check_jwt_secret
+                with patch("SPARC.auth.JWT_SECRET", _DEFAULT_JWT_SECRET):
+                    # Should not raise (defaults to development)
+                    check_jwt_secret()
+
+                with patch.dict(os.environ, {"APP_ENV": "development"}):
+                    importlib.reload(SPARC.config)
+
+
+class TestCORSConfig:
+    """Test that CORS origins are configurable via environment variable."""
+
+    def test_default_cors_origins(self):
+        """When CORS_ORIGINS is unset, defaults to localhost origins."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": ""}):
+            import importlib
+            import SPARC.config
+            importlib.reload(SPARC.config)
+            assert SPARC.config.cors_origins == [
+                "http://localhost:3000",
+                "http://localhost:5173",
+            ]
+
+    def test_custom_cors_origins(self):
+        """Setting CORS_ORIGINS configures allowed origins."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "https://sparc.example.com,https://app.example.com"}):
+            import importlib
+            import SPARC.config
+            importlib.reload(SPARC.config)
+            assert SPARC.config.cors_origins == [
+                "https://sparc.example.com",
+                "https://app.example.com",
+            ]
+            # Restore
+            with patch.dict(os.environ, {"CORS_ORIGINS": ""}):
+                importlib.reload(SPARC.config)
+
+    def test_single_cors_origin(self):
+        """A single origin without comma works correctly."""
+        with patch.dict(os.environ, {"CORS_ORIGINS": "https://sparc.example.com"}):
+            import importlib
+            import SPARC.config
+            importlib.reload(SPARC.config)
+            assert SPARC.config.cors_origins == ["https://sparc.example.com"]
+            with patch.dict(os.environ, {"CORS_ORIGINS": ""}):
+                importlib.reload(SPARC.config)