Normalize Turnstile env values

backend/config.js

@@ -1,6 +1,20 @@
 require('dotenv').config();
 
-const firstEnvValue = (...values) => values.find((value) => typeof value === 'string' && value.trim())?.trim() || '';
+const TURNSTILE_KEY_MATCH = /[0-9]x[0-9A-Za-z_-]{20,}/;
+
+const normalizeTurnstileValue = (value) => {
+    if (typeof value !== 'string') return '';
+
+    const trimmedValue = value.trim();
+    const keyMatch = trimmedValue.match(TURNSTILE_KEY_MATCH);
+    if (keyMatch) return keyMatch[0];
+
+    return trimmedValue.replace(/^[\s"'`{[]+|[\s"'`}\]]+$/g, '');
+};
+
+const firstEnvValue = (...values) => values
+    .map(normalizeTurnstileValue)
+    .find(Boolean) || '';
 
 const TURNSTILE_SITE_KEY = firstEnvValue(
     process.env.TURNSTILE_SITE_KEY,