Example integration with Terra missing about customauth

[misicnenad]

Found a solution to the issue:
CustomAuth basically returns a private key for user on frontend, so we can derive terra private key by using CustomAuth private key as entropy.

Example to do this is:

const { MnemonicKey } = require('@terra-money/terra.js');
const bip39 = require('bip39');

const torus_key = "cb8b467539d992dd1510bbe0e69a3b654ada325fbe4d830d0fbeab7788bc296f";

const mnemonic_phrase = bip39.entropyToMnemonic(torus_key);

const mk = new MnemonicKey({
    mnemonic: mnemonic_phrase, // optional, will be random if not provided
    coinType: 330, // optional, default
    account: 0, // optional, default
    index: 0, // optional, default
});

console.log("account 0, index 0 key", mk.privateKey.toString('hex'))

In above code snippet just replace the torus_key with the one returned from CustomAuth.