Abstract: A facility providing securely for a multi-tiered server-implemented application is described. The facility receives in a back-end application service a request from a front-end application service. The request includes both (1) a first security token obtained by a client that called the front-end application service, which identifies as its audience the front-end application service, and (2) a second security token obtained by the front-end service identifying the back-end service as its audience. The facility validates the first and second security tokens. Where the first and second security tokens are both successfully validated, the facility performs the received request in the back-end application service. Where the first and second security tokens are not both successfully validated, the facility returns an error.