/**

• Middleware to authenticate JWT tokens in incoming HTTP requests.
• Extracts the Bearer token from the Authorization header, verifies its validity,
• and attaches the corresponding user object to the request if authentication succeeds.
• Responds with appropriate HTTP status codes and error messages if:
• • The token is missing (401 Unauthorized)
• • The token is invalid or expired (403 Forbidden)
• • The user associated with the token does not exist (404 Not Found)
• @param {Object} req - Express request object, expects authorization header and mongoose instance.
• @param {Object} res - Express response object, used to send error responses.
• @param {Function} next - Express next middleware function.
• @returns {void} */