I'm creating a custom adapter, and i'd like to know if it's possible to access the headers of the request from the adapter ? I have a header for the url of the db of the tenant, placed by a middleware, so before that better-auth gets the request. I'm building a database adapter for postgREST (use fetch calls to communicate with a db pg) and i'd like to use the request's headers so that better-auth communicates to the right database, thus supporting multi tenancy without breaking better-auth's inner processes... @Better Auth