How to transfer (using Program instructions) custom SPL token from my own account to another user's wallet?

Question

This is my situation:

1. I have created a wallet

   solana-keygen new

2. I have created my own custom SPL Token

   spl-token create-token

3. Then I created an Account for this SPL Token

   spl-token create-account

4. The SPL token is now in my wallet A

In the Solana Program, I would like to programmatically transfer the custom SPL token from Wallet A to Alice(user) wallet when certain conditions are met (for example, when Alice answered a quiz correctly, she will be awarded some custom SPL token).

How do I authorise the Solana Program to deduct from Wallet A (which I had created) and transfer the tokens to Alice wallet?

Please advise me how to go about doing this. Really appreciate this.

Answer 1

To transfer an SPL token within a program, your best option is to have wallet A owned by a program-derived address, and then your program can transfer the tokens from wallet A based on any logic it wants.

So first, transfer the ownership to your program-derived address:

spl-token authorize <WALLET_2_ADDRESS> owner <PROGRAM_DERIVED_ADDRESS>

Then in your program, you can transfer to Alice with something like:

let transfer_instruction = spl_token::instruction::transfer(
    &token_program.key,
    &wallet_a_token_account.key,
    &alice_token_account.key,
    &program_derived_account.key,
    &[],
    transfer_amount,
)?;

let required_accounts_for_transfer = [
    wallet_a_token_account.clone(),
    alice_token_account.clone(),
    program_derived_account.clone(),
];

invoke_signed(
    &transfer_instruction,
    &required_accounts_for_transfer,
    &[
        &[b"your", b"seeds", b"here",]
    ]
)?;

This was adapted from a full example for transferring SPL tokens within a program: https://solanacookbook.com/references/programs.html#how-to-do-cross-program-invocation

More information about program-derived addresses at https://solanacookbook.com/references/programs.html#how-to-create-a-pda, with an example of how to create an account.