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 CEX.IO account.
Navigate to the API Tab under your account settings.
Create a new API key by only checking the Account Balance box and click on Generate Key.
Save your UserId, Key, and Secret. These will all be needed to import using the API. Once you have it saved in a safe place, click the Activate button.
CEX.IO will then have you confirm this by sending you a 2FA code. Enter that code on the next popup.
After entering the code, you will also need to click the confirmation email they send to you.
Inside of CryptoTrader.Tax, navigate to the Import Trades step and click on the CEX.IO tab. Enter the API Key, API Secret, and UserId saved from earlier.
Finally, click the Import Your Trades button to begin the automatic import.