I used the standard IERC20 to create an ERC20 smart contract.

I made a gambling game, that if the current user loses, he/she will have to transfer one token to the dealer (also the deployer aka msg.sender of the smart contract).

With the scenario above, I think that transferFrom("CURRENT_USER_PRIVATEKEY", "DEPLOYER_PUBLICKEY", 1) should be the answer.

However, with web3js and and metamask, I'm not sure how to get the "CURRENT_USER_PRIVATEKEY", since Metamask won't allow web3js to get the private key. In other StackOverflow posts, I found that we can hardcode this privatekey, but it's not ideal for a system with several users. What should I do to execute this transferFrom() function?

Here is my smart contract and code for the transaction:

async playerLoseMoney(){
    // Transfer money from player to the dealer
    const AMOUNT = 1;
    try{
      const contract = await this.getContract(erc20_abi_json);
      const computerChoice = await contract.methods.TransferFrom(
        "0x8a2a3a1dacF2B4b57734eB3DB71c33d3EBe263B6",
        "0xc00432E08770B9be73fB2303203B407d7B2E2cf2",
        AMOUNT
      ).call();
      alert("You lose 1 coin!")
    }catch(err){
      alert(err.stack);
      window.location.reload(); 
    }
  }

contract ERC20Token is IERC20 {
    ....
    function transferFrom(address owner, address buyer, uint256 numTokens) public returns(bool){
        require(numTokens <= balances[owner]);
        require(numTokens <= allowed[owner][msg.sender]);

        balances[owner] = balances[owner].sub(numTokens);
        allowed[owner][msg.sender] = allowed[owner][msg.sender].sub(numTokens);
        balances[buyer] = balances[buyer].add(numTokens);
        emit Transfer(owner, buyer, numTokens);
        return true;
    }
}