So on my SAML IDP when you get sent here it tried a login if successfull you get send to landinguri.
But if the process fails - you get a new session and thus you lose landinguri
Personally I think its a pain that APM hides stuff behind /my.policy a lot of other SSO's use the destination path(url) in the url that way if you have to restart the process the destination is stil there - much nicier
How do other deal with login processes that get lost
