Modernization: Replace md5() with secure password hashing

Problem/Motivation

The MyrestTokenAuthProvider uses md5() for token verification, which is insecure and susceptible to various attacks.

Proposed resolution

• Replace md5() with a more secure hashing algorithm (e.g., SHA-256 via hash_hmac).
• Use hash_equals() for timing-attack-safe comparisons.
• Consider using Drupal's password service for managing these tokens.

Remaining tasks

Update the authentication provider logic and verify token validation.

User interface changes

None.

API changes

Internal token verification logic change.