Fix redirect URL

auth/actions.ts

···
 
 export async function login(formData: FormData) {
   const rawHandle = formData.get("loginHint") as string;
-  const returnUrl = (formData.get("returnUrl") as string) || "/";
+  let returnUrl = (formData.get("returnUrl") as string) || "/";
+  if (!returnUrl.startsWith('/')) {
+    returnUrl = '/'
+  }
 
   const handle = rawHandle?.trim().replace(/^@/, "");