Support for market-aware auth URLs in Customer Account API

You can now pass locale and region_country parameters to the Customer Account API authorization endpoint to build
market-aware login experiences in headless storefronts.

Liquid storefronts handle this automatically with {{ routes.account_login_url }}, but headless storefronts previously had no documented way to construct login URLs that respect market context. We've added documentation and support for two optional
authorization parameters:

• locale: Controls the language of the login screen. Supports regional variants like fr-CA and en-GB, which load market-specific translations set through Translate & Adapt.
• region_country: Controls the market context for policies, branding, and other non-translation content. Uses an ISO 3166-1 Alpha-2 country code.

These parameters can be used independently or together for a fully localized login experience.

Learn more about building market-aware auth URLs for headless stores. For the full list of authorization parameters, refer to the Customer Account API authorization reference.