How to display all site collections to users for site access

Question

Currently when our users clients/internal log in, they are directed to a site directory.  The site directory only displays sites that the users have access too.  Which is great because I don't want our clients to see our entire client list.  
Currently we have one site collection with 700+ sites.  
We are changing the architecture of our SharePoint environment to create a new site collection for each client.  So, we may have 700+ site collections in one web application.  
My question is, how can I display all site collections to our user for access, similar to a site directory?  
Any help would be greatly appreciated.  
Thanks,

Answer 1

This is not possible OOTB. your requirement is get the list of all site collections on root site then security trim( which means user can see only the sites where they have permission.)
I think this required alot of effort(developing a solutions and checking the permission on all sites). Issue is you have more than 700 sites collections and tons of user for each site collections and also 700+ clients.
May be think about creating a list and fill that with all site collections(using script). then trim configure the item level permission( but lot of work).
if you have user profile services then may be check about the memberships feature. 
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