FTS improvements for LHC Run-3 and beyond

The File Transfer Service (FTS) developed at CERN and in production since 2014, has become a fundamental component for the LHC experiments and is tightly integrated with experiment frameworks. Starting from the beginning of 2018 with the participation to the European Commission funded project eXtreme Data Cloud (XDC) and the activities carried out in the context of the WLCG DOMA TPC and QoS working groups, a series of new developments and improvements have been planned and performed taking also into account the requirements from the experiments in preparation for the LHC Run-3. This paper provides a detailed overview of these developments; more specifically, the integration with OpenID Connect (OIDC), the QoS integration, the service scalability enhancements, the support for XRootD and HTTP Third Party Copy (TPC) transfers along with the integration with the new CERN Tape Archive (CTA) system.