When a web application is connected to Phantom, it can also request that the user signs a given message. Applications are free to write their own messages which will be displayed to users from within Phantom’s signature prompt. Message signatures do not involve network fees and are a convenient way for apps to verify ownership of an address. To learn how you can use libraries such as ethers.js to abstract away some of these intricacies, see handleSignMessage in our sandbox. 
const message = 'To avoid digital dognappers, sign below to authenticate with CryptoCorgis.';
const from = accounts[0];
const msg = `0x${Buffer.from(message, 'utf8').toString('hex')}`;
const sign = await provider.request({
        method: 'personal_sign',
        params: [msg, from, 'Example password'],
    });

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Support for “Sign-In with” standards

Applications that rely on signing messages to authenticate users can choose to opt-in to one of the various “Sign-In with” (SIW) standards. For more details, see Sign-In with (SIW) standards.