Custom OIDC Providers for Supabase Auth

Supabase Auth now supports the integration of custom OpenID Connect (OIDC) providers, allowing users to authenticate through identity providers not covered by the over 20 built-in social providers like Google or GitHub. This feature enables organizations to incorporate regional or self-hosted identity solutions, ensuring compliance and meeting specific needs. Once a custom provider is set up, the authentication process for users remains consistent with built-in providers, as the Supabase auth server manages the complete OAuth flow, including token exchanges and user profile fetching. The setup involves supplying the provider's issuer URL, client credentials, and scopes, with Supabase automatically handling the discovery of necessary endpoints and JSON Web Key Sets (JWKS). Additionally, Proof Key for Code Exchange (PKCE) is enabled by default to enhance security, and configurations can accommodate multiple platforms and providers that do not return email addresses. Users can create and manage custom providers through the Supabase Dashboard or the auth Admin API, with up to three custom providers per project, and further support available if needed.