Idea Summary
I want to link to an APEX app detail page from another system. And I want my users to not have to open such a link.

As it is a detail page, I need to pass an ID. When I understand Enabled for All Sessions (and my tests) correctly, there is no way of passing that ID without a checksum. As I can't compute a checksum from the other system, I am screwed.

I see that there are a lot of security implications with that. But in my case the page I am linking to is read-only and has security checks that filter out data if the user is not logged in/unauthorized. 

Just killing a session where the user has to log in again is user hostility and makes sure users dislike the app. I respect default settings that make APEX secure, but I think there has to be a way for developers to make something like this possible when they know the risks and are prepared for them. In this case, APEX as a framework is in the way of achieving a nice experience.

Preferred Solution
Add a new Rejoin Sessions level (maybe just on a page level) that allows you to have no checksums.

For anybody else with that issue: I am now using a workaround where I pass the page item as a hash route instead of a query parameter and then parse that with JS  to finally set the page item.