I cannot speak to the concept of a "temporary" EU Digital Covid Certificate in other parts of Europe, but in The Netherlands, you have to be a Dutch citizen or holder of a long-term residence visa. You also have to have a DigiD account, which stands for Digital Identity. With your DigiD you show who you are if you want to arrange something on the internet with a (semi) government organization. Examples would include the tax authorities, education, healthcare, or your pension fund. So basically, you're registered with the government in some fashion. It would be interesting to hear about how other countries are handling the "security and access" of the EU Digital Covid Certificate process and who does allow "temporary" access.
Currently - and who knows what will be the process in March 2022 - you do need to complete the EU Digital Passenger Locator Form (dPLF) to enter Italy, regardless of whether you have the EU Digital Covid Certificate or you are traveling on a non-EU vaccination card. (I am going in a few weeks, and although I have a EU Digital Covid Certificate, I have already completed & submitted my dPLF application).
As ChristineH mentions, currently, the CDC vaccination card will work in Italy for access/entry. It seems that traveling these days is a constant checking - and updating - of the rules and procedures for your outbound and return country policies. For example, today only three countries are using the EU Digital Passenger Locator Form (dPLF). Who knows if that will be the case in 2022. And if you're traveling between countries in the EU, you also have to check the entry requirements for the country next on your list and how those rules pertain to where you're coming from. And no, unfortunately, they are not all the same. COVID has certainly had an impact on Schengen policies and the concept of open borders.