Before diving into Shopify App and API documentation, I would like to ask to your team if Shopify allows a Customer Authentication System to be totally based on an external services ( credential at least) ... like REST API, or something like that ?
One of the main concern of our client is to keep its actual authentication service and plug it on the chosen e-commerce solution. Do you think it 's possible with Shopify ? Do you have any readings that allow us to go faster in it ?
Thanks for your help.