Sponsored signer rotation
Add a new key as signer of the account and set the master key to weight 0, keeping the same G... address. The app pays the 0.5 XLM reserve and the fee.
Log in with Demo key
Freighter and the Stellar Wallets Kit wallets can only sign with their master key: once the rotation sets it to weight 0, you lose access to the account. This page only runs with the Demo key adapter, which can switch to the new key.