Authentication Integration with existing website

[marc_occa]

I have a existing website with an authentication flow (sign in, sign up and so on).
I would like to integrate with Shopify in a way that only signed up users from my site could access the shopify store.
I saw multipass solution but at this point Shopify Plus is out of my price range.

So I though I could integrate using the GraphQL API.

Here is a high level design of this solution.

1. When a new customer creates an Account on my website I would send a request to my Shopify store to create an account as well.
2. I would have link on my site to send the customer to the shopify store.
   1. This link would send a resquest to get  an authentication token
3. I would send the user to the shopify store with the authenticated token. 

Does this make sense and can it be accomplished as described?