Supabase is an open source Firebase alternative. Start your project with a Postgres database, Authentication, instant APIs, Edge Functions, Realtime subscriptions, and Storage.

Supabase

I guess it has been asked 1000 times, but I can't find it 🙈  

I'd like to set the login / redirect URI dynamically - depending on the current host / site. I'm working with feature branches (vercel) so each feature has it's own preview URL. 
```supabase.auth.signIn({ email }, { redirectTo: "URL here" })```  // does supabase follow this `redirectTo`?

Yes but you need to make sure the redirectTo URL is listed under your additional URL inside of the Supabase UI.

Hmm, but how do I dynamically update the URL in the supabase config?

You cannot, it has to be static, you can only dynamically generate a url for the redirectTo