How is the expiryTime supposed to be used with SessionSecurityTokenCache.AddOrUpdate()?

问题

I'm writing a custom implementation of SessionSecurityTokenCache and I'm somewhat confused as to what the purpose of expiryTime is in the AddOrUpdate method.

As far as I can tell, the default implementation for SessionSecurityTokenCache used by WIF is the internal class MruSessionSecurityTokenCache (mentioned here). In its implementation, expiryTime is completely ignored.

Also, I notice while debugging that the value that gets passed in to AddOrUpdate appears to always be token.ValidTo plus 5 minutes, so there is some intent to use this value somehow.

A few questions:

• What is the intended strategy for this value?
  
  • Occasional cache cleanup?
  • Should the Get() and GetAll() methods on SessionSecurityTokenCache be filtering out expired tokens?
• In any of these cases, why not just use SessionSecurityToken.ValidTo (or some offset therefrom)?

来源：https://stackoverflow.com/questions/16122332/how-is-the-expirytime-supposed-to-be-used-with-sessionsecuritytokencache-addorup