Best option to implement external register/login to WP from self-made API

Question

Hi everyone and thank you in advance for reading the question and helping me out.

I amb building with a friend an app that uses a custom self-made PHP-MySQL API to be cross-platform. Everything in the app works thanks to that API but we need users to be controlled by an external WP. WP and API are in different sub-domains and servers.

So we have: WP (for users) + API (for functionalities and data) + Apps (UIs).

Users write it's credentials in the App and that credentials go to our own API and here is where I doubt how should I use those credentials to log in into WP. The same happends to register. Those two functionalities need to be handled by WP and I don't know which of this 2 options is best:

Option 1: Create another mini-api for WP with wp_create_user() and others needed and call from the main API to the mini-api for WP to regiser / login

Option 2: Use WP Rest API to authenticate and register. The problem with that option is that all the examples that I have seen were web-based and I need to implement it with no grafic interfice to call it from my PHP API.

Response needed: In any case the only answer I need from WP is the wp_user id.

PD: Sorry for my poor english, it's not my native language

Answer 1

Option 1: Why create your own WordPress API (mini or not) when you already have one?

Option 2: You should try to extend the WordPress REST API in order to register/authenticate. You can use, e.g. https://es.wordpress.org/plugins/json-api-user/ or just grab from it the code you need and modify it.