Twilio has introduced HTTP Basic and Digest Authentication, allowing users to password protect their TwiML URLs on their web servers, ensuring only authorized access. This feature uses a URL format with a username and password, which Twilio will authenticate using the provided credentials. To enhance security, Twilio also cryptographically signs its requests using HMAC-SHA1 and the AuthToken, verifying the authenticity of incoming requests by re-assembling the data string and comparing it to the received signature. Users are advised to use SSL with this feature for added protection against malicious third-party access.