It is not mandatory to perform client authentication by means of a digital certificate for the creation / validation of the Time Stamp. However, what is mandatory is to have previously applied to the service to use it. You can consult the procedure for applying for the validation service and Time Stamp by accessing the Services route on the AOC Consortium website - Services - Valid - once in this section, go down to “Services that are part of the Valid” and select "Validator" -Learn more
You will find the following registration form:
Registration form for the Validator service and the Time Stamp