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In the Twilio API keys overview, Twilio says API keys are the preferred way to authenticate with Twilio REST APIs. Create a key in the Twilio Console via Create API Keys in the Console. Use the API Key SID as the HTTP Basic username and the API Key Secret as the HTTP Basic password.

For local testing, Twilio documents that you can use your Account SID and Auth Token as API credentials. Get them from your Twilio account in Console and manage them from REST API: Auth Token. Use the Account SID as the HTTP Basic username and the Auth Token as the HTTP Basic password. Twilio recommends API keys instead for production.

Create an OAuth app in the Twilio Console using OAuth apps. Twilio generates a Client ID and Client Secret. Use them with the OAuth client credentials grant at Twilio's token endpoint to obtain a short-lived access token, then send that bearer token to supported Twilio APIs. Twilio notes these tokens currently expire after 1 hour and are scope-limited.