Since July 2017, the WLCG Authorization WG has been looking into how authentication and authorization technologies used on WLCG may evolve towards taking advantage of federated identities and standards commonly used in industry and academia, in particular through the use of JSON Web Tokens (JWT). Notable results include the publication of the WLCG Common JWT Profiles and the WLCG Bearer Token Discovery specification. This document aims to define milestones concerning technical aspects of the transition from X509 proxies with VOMS attributes toward the use of WLCG tokens in all relevant workflows. These milestones are tentative.