Don't know how to make app in wix for given definition

Question:
I want to make a wix app. This app will trigger the 3rd party API when any user login in the website. can this is possible with wix blocks ?

I have tried with webhooks, and react-sdk combined, but in that I don’t know how I will store the credentials of 3rd party API

You can use the Secrets API/SDK.

REST: Introduction | REST

SDK: Secrets Setup | SDK