External logins (OAuth, OpenID Connect)?

Short answer: Use built-in providers: services.AddAuthentication() .AddGoogle(options => { options.ClientId = "..."; options.ClientSecret = "..."; }); Also supports: Facebook Microsoft Twitter OpenID Connect Azure AD Use RemoteAuthenticationHandler<T> or Identity scaffolding.

Example code

Use built-in providers: services.AddAuthentication() .AddGoogle(options => { options.ClientId = "...";
options.ClientSecret = "..."; }); Also supports: Facebook Microsoft Twitter OpenID Connect Azure AD Use RemoteAuthenticationHandler<T> or Identity scaffolding.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.