### Context
I'm Alpha server, and I can grant permission to access things on Beta server at any point in the future, but I can only talk with Beta server one time, during initial setup (to share a secret, etc.).
Gamma server can talk to me and to Beta server any time. I can also give Gamma server instructions.
### Scenario
Gamma server comes to Beta server and says, "let me in". Beta server says, "go ask Alpha server for permission and return with proof of permission".
### Question
How can the above scenario be achieved? Does this type of permission mechanism already have a name? Would it simply require some shared secret between Alpha server and Beta server and some sort of hash calculation?
I'd also like the permission to expire after a certain period of time (or at a specific datetime).
### Notes
I realize this has similarities to OAuth 2, but since Alpha server can only speak to Beta server one time ever (initial setup), OAuth 2 cannot be used.
I'm Alpha server, and I can grant permission to access things on Beta server at any point in the future, but I can only talk with Beta server one time, during initial setup (to share a secret, etc.).
Gamma server can talk to me and to Beta server any time. I can also give Gamma server instructions.
### Scenario
Gamma server comes to Beta server and says, "let me in". Beta server says, "go ask Alpha server for permission and return with proof of permission".
### Question
How can the above scenario be achieved? Does this type of permission mechanism already have a name? Would it simply require some shared secret between Alpha server and Beta server and some sort of hash calculation?
I'd also like the permission to expire after a certain period of time (or at a specific datetime).
### Notes
I realize this has similarities to OAuth 2, but since Alpha server can only speak to Beta server one time ever (initial setup), OAuth 2 cannot be used.