post https://api.fabric.inc/v3/oauth2/default/v1/token
After a User App is created, the merchant receives a login URL. By using this URL, along with the Client ID, Client Secret, and storefront credentials, the system generates a headless user token. This token is created specifically for User Apps with a usageType of api. This endpoint supports the OAuth2 password grant flow to allow client authorization through the User App, which already holds the shopper's credentials.