add session secret for signing

Author: kentcdodds

app/routes/resources+/theme/theme-session.server.ts

@@ -6,6 +6,7 @@ export const sessionStorage = createCookieSessionStorage({
 		sameSite: 'lax',
 		path: '/',
 		httpOnly: true,
+		secrets: [process.env.SESSION_SECRET],
 		secure: process.env.NODE_ENV === 'production',
 	},
 })