Is there a way to import contacts to a web app?

For a programming class assignment (working with team consisting of users with experience in Java, PHP, .NET, MySQL, and C#), we decided to try building a basic version of a social media website (like a Twitter or Facebook clone). One of the features we wanted to try adding was a way to import contacts to the site to either invite the contacts to create an account (not really implemented due to smaller assignment scope, but just given as an option) or to check if the contact already had an account on the site (through email or name-checking).

We've seen that there's a way to do this through Android app development and permissions in Java, but we can't find much information on how to implement this on a web app. Is this possible? The closest we've come to a solution is through having the user simply enter the emails of the user they want to invite to the site (mostly through Mailchimp audiences).

Any tips or guidance would be greatly appreciated.

Thank you.

This post maybe not your answer directly but you need to know:

There are plenty of solutions for contact discovery! Just search this keyword: Contact Discovery.

However, I strongly suggest you consider privacy at the first of developing your app, because users cannot allow you to find their contacts in clear. You can use secure methods to contact discovery.

I suggest you find methods on signalapp:
https://github.com/signalapp/ContactDiscoveryService .
This written in Java and is very secure but a little hard to understand.
Please take a look at Private contact discovery for Signal to get idea.