I've implemented my action using Google Sign-in and Account Linking but I've realised that this may not be necessary as I just need to retrieve the user email address, name and last name during the conversation for the sole purpose of sending an email and forget about it after.
With account linking the user interacting with my agent is asked to "register" an account with which could discourage users to proceed.
I've found this agent which simply asks "in order to get your email address can we access your google account"... https://assistant.google.com/services/a/uid/000000f63f47d43d
How can that be achieved?
Thanks, Salvo