[keycloak-user] How to set the user login in registration process.

Hi all, I would like to know if it possible to start the registration process by fixing the username (a specific email) in some cases (by giving a url param or something like that). In my app I send invitations to member's email and I'de like the user to use the same email during keycloak registration process so I want my app to redirect to registration form with this particular email as a readonly form param. I imagine I can provide a dedicated template allowing the username email readonly in some cases but I can't figure how to access url specific parameters in this template ? Thanks for your help, best regards, Jérôme.