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I think it's a pain because it's one of those things you just can't guarantee. I can (try to) promise you as an IdP that website X can't just randomly ask for y

I think it's a pain because it's one of those things you just can't guarantee. I can (try to) promise you as an IdP that website X can't just randomly ask for your information and be given it without your consent. But once I've given that information away, it's irreversible. You can't unsend data. You can ask nicely for it to be deleted, or revoke future access, but unless you have a time machine, federated SLO for all parties in a session ought to just be considered an impossibility, and planned for accordingly with short sessions.

londons_explore 6y ago
> But once I've given that information away, it's irreversible. In an enterprise environment all software has a basic level of trust of "this will try to do what it claims to do". That means the ID provider can directly ping the server of whatever service was issued the data or login cookies and say "this data should be deleted please".
- hunter2_ 6y ago
  If you administer every SP, it starts to become a possibility. But as TFA mentions right off the bat, that's atypical. And even if you do exclusively use SPs that support SLO, is the user supposed to wait while the IdP does all of that outreach in order to know that it worked, or 97% worked because one timed out? That depends on whether the user should even care about the outcome -- if they should care, then do they get an email when it achieves 100% hours/days later when that down-at-time-of-SLO SP is back up? Should they report an incident if they never see a success report?
  - 35fbe7d3d5b9 6y ago
    > But as TFA mentions right off the bat, that's atypical. So atypical that it borders on inconceivable. There's almost always an external party in there. But if you somehow end up totally internal sure, try the back-channel binding. You get to toss SOAP messages around, and it might work. Of course now one of the invariants you built around no longer holds ("SAML works without having to let the IdP talk to the SPs" oh my sweet summer child...) Just don't try SLO over the front channel, or else you'll have the joyous UX of a user clicking "log out" and all of a sudden they're bouncing logout messages back and forth between the IdP and two dozen internal applications. Hope the ninth app in line isn't down for maintenance or your <LogoutResponse> never makes it back to the IdP and the user wonders why they're staring at a server error page for an app they haven't used in hours and why half their environment is logged in and the other half isn't...

londons_explore 6y ago

> But once I've given that information away, it's irreversible. In an enterprise environment all software has a basic level of trust of "this will try to do what it claims to do". That means the ID provider can directly ping the server of whatever service was issued the data or login cookies and say "this data should be deleted please".

hunter2_ 6y ago
If you administer every SP, it starts to become a possibility. But as TFA mentions right off the bat, that's atypical. And even if you do exclusively use SPs that support SLO, is the user supposed to wait while the IdP does all of that outreach in order to know that it worked, or 97% worked because one timed out? That depends on whether the user should even care about the outcome -- if they should care, then do they get an email when it achieves 100% hours/days later when that down-at-time-of-SLO SP is back up? Should they report an incident if they never see a success report?
- 35fbe7d3d5b9 6y ago
  > But as TFA mentions right off the bat, that's atypical. So atypical that it borders on inconceivable. There's almost always an external party in there. But if you somehow end up totally internal sure, try the back-channel binding. You get to toss SOAP messages around, and it might work. Of course now one of the invariants you built around no longer holds ("SAML works without having to let the IdP talk to the SPs" oh my sweet summer child...) Just don't try SLO over the front channel, or else you'll have the joyous UX of a user clicking "log out" and all of a sudden they're bouncing logout messages back and forth between the IdP and two dozen internal applications. Hope the ninth app in line isn't down for maintenance or your <LogoutResponse> never makes it back to the IdP and the user wonders why they're staring at a server error page for an app they haven't used in hours and why half their environment is logged in and the other half isn't...