How it manage private keys truffle?

Question

I'm trying send tokens in mi custom contract which is deployed in ropsten. Also, I'm working with truffle and truffle-contract 1.1.11 library. My doubt is, how should I sign transactions inside the environment of truffle?

On other hand, if it possible, I would like know how is truffle managing the private keys, because when I set up the project on local ganache blockchain all my stuff works. When I try to sign a transaction from another address different from the contract deploy address, it just magically guest private keys. This of course is in ganache but the problem is in ropsten.

pragma solidity ^0.5.0;

import "@openzeppelin/contracts/token/ERC20/ERC20Detailed.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Mintable.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Burnable.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Pausable.sol";

contract CustomToken is ERC20Pausable, ERC20Burnable, ERC20Mintable, ERC20Detailed {

    constructor () public ERC20Detailed("CustomToken", "CT", 2) { }

    // some functions who call super.function(), this reproduces default behavior of a base ERC20 token

}

const contract = require('truffle-contract');

const customtoken_artifact = require('../build/contracts/CustomToken.json');
let CustomToken = contract(customtoken_artifact);

module.exports = {

    sendCoin: function(amount, sender, receiver, callback) {
        let self = this;

        CustomToken.setProvider(self.web3.currentProvider);

        let custom;

        CustomToken.deployed().then(function(instance) {

            custom = instance;

            return custom.transfer(receiver, amount, {from: sender});

        }).then(() => callback("202"))
            .catch(function(e) {
                console.log(e);
                callback("400 " + e);
            });
    },
};

Finally, I expect know how is truffle managing the private keys or when I should sign the transaction.

Answer 1

To sign transactions in Truffle you can use HDWalletProvider :

https://www.npmjs.com/package/@truffle/hdwallet-provider

You can configure it in your truffle-config.js

Answer 2

Create a truffle-config.js file:

require('dotenv').config();

let PrivateKeyProvider = require("truffle-privatekey-provider");

module.exports = {

    networks: {
        kovan: {
            provider: new PrivateKeyProvider(process.env.KOVAN_PK, process.env.KOVAN_PROVIDER),
            network_id: 42,
            from: process.env.KOVAN_ACCOUNT,
            gas: 8000000
        },
    },
    // Set default mocha options here, use special reporters etc.
    mocha: {
        timeout: 100000
    },
    // Configure your compilers
    compilers: {
        solc: {
            version: "0.5.12",
        }
    },
};

And then you may store the provider, account and private key in a .env file called:

# Kovan Test Network
KOVAN_PROVIDER=https://kovan.infura.io/v3/76b...
KOVAN_ACCOUNT=0xE...
KOVAN_PK=1a..