I'm trying to make some changes to customer registration. The idea is to add some custom fields to the registration - I understand the concept of metafields and I know how to do a GraphQL query to create a consumer with metafields.
What I don't understand though is how can I parse the input from the consumer to create the consumer account together with the custom metafields. I can imagine I need to add a way to configure graphql credentials and execute a graphql query after the "submit form" button is pressed on the website, but I can't figure out what does the website do during the registration right now - customers/register.liquid only defines how does the registration form look like, what are the inputs.
So the question is: Where do I find what happens on the backend after the consumer submits the registration form and how can I modify that?