Identity Provider — Simple#

Problem statement (interviewer prompt)

Design an OAuth2 / OIDC identity provider that other apps integrate with for single sign-on. Cover the authorization code + PKCE flow, refresh + access tokens, JWT vs opaque tokens, session management, social login federation, and multi-factor auth.

flowchart LR
  U([User])
  APP[App]
  IDP[Identity Provider]
  TOK[Token]
  U --> APP
  APP --> IDP
  U --> IDP
  IDP --> TOK --> APP
  APP --> U

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class U client;
    class APP,IDP,TOK service;