WLCG Token Usage and Discovery

<!--HTML-->Since 2017, the Worldwide LHC Computing Grid (WLCG) has been working towards enabling token based authentication and authorisation throughout its entire middleware stack. Following the publication of the WLCG v1.0 Token Schema in 2019, middleware developers have been able to enhance their services to consume and validate OAuth2.0 tokens and process the authorization information they convey. Complex scenarios, involving mul- tiple delegation steps and command line flows, are a key challenge to be ad- dressed in order for the system to be fully operational. This paper expands on the anticipated token based workflows, with a particular focus on local storage of tokens and their discovery by services. The authors include a walk-through of this token flow in the RUCIO managed data-transfer scenario, including delega- tion to FTS and authorised access to storage elements. Next steps are presented, including the current target of submitting production jobs authorised by Tokens within 2021.