You can now password protect your TwiML URLs on your web server using HTTP Basic or Digest Authentication with Twilio, allowing only authorized access to secure data. To ensure authenticity of requests from Twilio, use SSL and verify the X-Twilio-Signature header by re-assembling the request data string and signing it with HMAC-SHA1 using your AuthToken as the key. This security measure protects sensitive data and prevents malicious third-party access to your web application.