Virtualized multi-tenant programmable switches enable on-demand support of different users' protocols and programs. However, supporting multiple tenants on a virtualized switch raises concerns such as resource isolation and security. Truly isolating users is mandatory for virtualized programmable switches to be deployed in production networks. In this paper we propose MTPSA, a Multi Tenant Portable Switch Architecture. MTPSA offers performance, resource and security isolation. It further introduces roles and privileges within programmable switches. MTPSA is an open-source contribution, implemented over PSA and NetFPGA. Our evaluation shows that it adds minimal overheads, supports line-rate throughput, and scales with the number of users, while providing an isolation of users.