More clarity on how this app should be used for to provide authentication for a startup business using Elixir/Phoenix

I'm building a phoenix app and I'm interested in a user login system. I will need to connect with my users' Google.com accounts and Telegram.org accounts, so I need something that gives me a bit more power that `phx.gen.auth` (which I also don't like because it clutters up my codebase).

It is taking me a long time to understand how I would use this package to provide authentication for my app, however -- this is not a library that I can add to my app's `mix.exs` file, for instance.

What I have gathered so far is that I will need to run two phoenix apps: my own app that I am interested in providing authentication for, and also this app, which will have to be deployed at another domain, perhaps auth.tadasajon.com if my app is running at tadasajon.com.

What I will then have is essentially an OAuth login system that I will use from my own phoenix app, and that potentially other websites can use as well if they would like their users to be able to login with their tadasajon.com accounts for some reason.

The way my Tadasajon.com app will use this app is through the `auth_plug` library, which I will add to my `mix.exs` file in my Tadasajon app.

Do I understand this correctly so far?

Also, I noticed that this codebase is under the GNU General Public License v2.0 -- I am not building free software, however. I'm just building a website that people are going to log in to and then pay me money so my partner and I can make a million dollars. It is not my intention to distribute the software I am building or to make it open source -- I only intend to provide a service to users who want to buy widgets. So I just want to be sure that this licensing does not require me to forsake making any money and also does not require all the code that I write to be open source.

Thanks!