The Twilio API uses HTTP Basic authentication to authenticate requests. Your Twilio Account SID will serve as the username, and your Auth Token as the password. These credentials - Account SID and Auth Token can be found on your dashboard as seen in the image below.
Below is a sample authenticated request to the Accounts resource:
curl -G https://api.twilio.com/2010-04-01/Accounts \
-u <YOUR_ACCOUNT_SID>:<YOUR_AUTH_TOKEN>
Please refer to our security documentation to learn more about how Twilio handles authentication.