For URL redirection, we must use URL redirector in Mendix, which you are using it already.
What info are you showing in the popup page and why do you want to show any information?
IMHO, this popup will be a empty popup only, with data view and URL redirector with in that and takes an attribute from the entity of dataview. Probably for better presentation, you could show some message like redirecting to One login.
Im not sure if I understood your question right. Can you explain it a bit more with screenshots?
One more additional solution I could think off, but it is up to you to check how it might work: you could use default logout in Mendix which takes the user to login.html. In the login.html, you could do the redirect to one login as well. Once again, it could be a blank page.