Creates an OAuthServerProvider that proxies OAuth flows to an
upstream authorization server using server-side callbacks.
This is the generic extraction of the server-side callback pattern —
all provider-specific logic is encapsulated in the options (endpoints,
scopes, mapUserInfo). The boilerplate (client store, state mapping,
callback handler, token exchange, TTL management) is handled here.
Creates an OAuthServerProvider that proxies OAuth flows to an upstream authorization server using server-side callbacks.
This is the generic extraction of the server-side callback pattern — all provider-specific logic is encapsulated in the options (endpoints, scopes,
mapUserInfo). The boilerplate (client store, state mapping, callback handler, token exchange, TTL management) is handled here.