Does somebody has a working confirguration to run Neos within a nginx alias?
domain.de/ other application
domain.de/cms/ root directory for neos
You can try to do it with an nginx proxy … but not sure if it will work.
Just curious, but why did you spend time on hiding the product ?
the reason is to extend an onlineshop with cms pages:
domain.de/ = onlineshop
domain.de/cms/ = extend the online shop with neos cms pages
(its a very simple integration without heavy adjustments)
So sorry I misunderstood your needs 
I understand that you don’t want to use the /neos to the backend.
I never try this setup personally, but a proxy to an other vhost that run Neos, should work. Not sure, but maybe this feature will be of interest for you: https://jira.neos.io/browse/FLOW-414?filter=-1 You can watch the Jira, I should work on it during next weeks.
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