To protect access to the signature page you already had the possibility to define a static validation code that you had to communicate to your user for use during access to the signing process.
This validation code can be dynamic and of a single use, OTP one-time-password, sent to the user by two possible channels: Email and SMS, and whose validity will be of 5 minutes. Once this deadline has passed, the code will be invalidated.
In the integration guide you have available a new chapter with the explanation of use.
https://doc.viafirma.com/documents/api/latest/es/validateCode.html
This new OTP protection feature is only available for web signing processes, using signPage. Soon it will also be available in signature processes from the Viafirma APP. You can make use of this configuration both from the API and from the template configuration.