Send and verify signature sign by user when sending POST request to server

[ken-futureverse]

Details here https://polkadot.js.org/docs/extension/cookbook/#sign-a-message

// this injector object has a signer and a signRaw method
// to be able to sign raw bytes
const signRaw = injector?.signer?.signRaw;

if (!!signRaw) {
    // after making sure that signRaw is defined
    // we can use it to sign our message
    const { signature } = await signRaw({
        address: account.address,
        data: stringToHex('message to sign'),
        type: 'bytes'
    });
}