Your third solution basically reinvents Kerberos. I don't think Kerberos envisioned services making calls to each other though. In the 1980s, I think it was ass

Your third solution basically reinvents Kerberos. I don't think Kerberos envisioned services making calls to each other though. In the 1980s, I think it was assumed that the client would contact each service separately and combine the results itself.