Proof Key for Code Exchange by OAuth Public Clients - Implementation - React Native - Expo - SPA - OAuth2

Summary Implementation / Adoption of RFC 7636 (Proof Key for Code Exchange by OAuth Public Clients) This feature request proposes integrating native support for PKCE (Proof Key for Code Exchange) in Directus to enhance OAuth2 flows, particularly for native and mobile applications. PKCE provides an additional layer of security by ensuring that the entity that initiated the OAuth2 flow is the same one completing it, preventing interception and code injection attacks. Implementing an abstraction layer for PKCE for directus: Basic Example Native App or SPA will create: • a random secret • the hash of the secret The native app or SPA will call POST: Body: • (e.g. google) • (a hash of a private secret) • (e.g. S256) • Then directus checks if provider is set, the redirect is allowed. Now the directus magic happens and the user is redirected to the provider and the normal Auth Flow (OAuth2) is performed. Directus redir…