CryptoTrader.Tax only needs "Read" or "View" access to import your trade history. This permission protects your accounts. Learn more about API access in this article here.
Login to your Bitstamp account.
Navigate to the API Access page: https://www.bitstamp.net/settings/access-control/api/
Click the New API Key button on the top-right and turn on the following permissions:
This will give CryptoTrader.Tax read-only access to your account and will not give access to your funds)
After submitting, make note and copy your API and API secret as they will be needed to import. Once both values have been copied, click on the Activate button.
Bitstamp will send you a confirmation email to complete activation.
Navigate to the Bistamp tab inside CryptoTrader.Tax and enter your API Key and API Secret into the the provided text boxes.
Finally click Sync Transactions to import your transaction history.