Support multiple supabase backends

Context I am using 2 separate supabase backends for different parts of an application. This provides a clear separation of data ownership and makes auditing access trivial. Each system has it's own auth providers - the user may have different email/passwords in each system - and the application is responsible for maintaining sessions with both backends, using the correct backend for different pieces of data. Supabase mostly supports this, except for in the way that tokens are delivered and validated by the GoTrue client. Tokens During a login, supabase returns a token in the form access_token=XXX;expires_in:Y;refresh_token:Z;token_type:bearer. This is stored by default in session storage under a key like sb-<unique-subase-id>-auth-token. Having multiple supabase clients is possible, as each looks for its own session storage token and works correctly. However, when logging in to supabase backend B, supabase backend A removes its token from storage. I beli…