[keycloak-user] Send parameter back after registration

Hello, I was wondering if there is a way for me to send a parameter back to my server after a new user registers in Keycloak. For example, we have a checkbox that the user can check if he wants to receive newsletter from our website, and I wanted to send that value back to us. I tried setting it as a query parameter on the redirect_uri param, it gets sent on the request, but it isn't posted back to us. Is there a defined way to accomplish this? Thank you again! -- Rodrigo Sasaki