Trying to solve no-duplicate-login issue, need to know how to stop or kill a login session.
Products.NoDuplicateLogin does not work on Plone5.1, so have to do it.
Thanks.
Whether this is possible depends on details of the acl_users configuration.
The standard acl_users session plugin implements "login session" via a cookie - and session termination by invalidating(deleting) this cookie. As cookies are maintained in the browser process, it is impossible to invalidate them in a foreign browser process. You would need an alternative plugin implementing "login session". It would still use a cookie (to identify the browser) but check its value against local data. You could then change that local data to let this check fail in the future and thereby effectively terminate the "login session".
Why do you need to solve this "problem"? What is the particular reason why you would not allow multiple logins.
Plone does not care and Plone does not track logins.
Does not works means exactly? Installation issue or?
This Plone web app is a subscription model, owner does not want user to share their logins.
Products.NoDuplicateLogin can be install in Plone5, no error but does not work at all.
It pass all the tests in Plone4 but fails all in Plone5.
How does it fail on Plone 5?
Products.NoDuplicateLogin is a PAS plugin, and does not give any error during run time.
The failures came from the package tests, not sure if it is useful dumping the error here.
When live with it if you do not want to share information 
To get the test failures, I just run
bin/test -s Products.NoDuplicateLogin
after install in Plone5.1.5
Total: 14 tests, 10 failures, 0 errors in 21.109 seconds.
Why don‘t you share the exact error information with the full tracebacks? Should we guess it???