validate_pdas.rs

// [get accounts] - user_ai, pda_ai
// regenerate the PDA
// seed scheme: ["arbitrary_seed", user's key]
let (pda, bump) = Pubkey::find_program_address(
	&[
		b"arbitrary_seed",
		user_ai.key.as_ref(),
	],
	program_id,
);
// OR if you have bump
let pda = Pubkey::create_program_address(
	&[
		b"arbitrary_seed",
		user_ai.key.as_ref(),
		&[bump],
	],
	program_id,
)?;
// throw error if account key doesn't match
if *pda_ai.key != pda {
	return Err(MyError::WrongPDA.into())
}