properly use OIDC security parameters like nonce and state

api/src/dooris_api/app.py

@@ -1,11 +1,16 @@
-#!/usr/bin/env python3
 from typing import Optional
+import logging
+import secrets
 from fastapi import FastAPI, Request, Response
 from fastapi.responses import RedirectResponse
-from pydantic import BaseModel
 from contextlib import asynccontextmanager
 from simple_openid_connect.client import OpenidClient
-from simple_openid_connect.data import TokenSuccessResponse, IdToken
+from simple_openid_connect.data import TokenSuccessResponse
+
+from dooris_api.models import UserStatus
+
+
+logger = logging.getLogger(__name__)
 
 
 @asynccontextmanager
@@ -19,16 +24,10 @@ async def lifespan(app: FastAPI):
     yield
 
 
-app = FastAPI(lifespan=lifespan)
-
-
-class UserInfo(BaseModel):
-    name: str
-
-
-class UserStatus(BaseModel):
-    is_logged_in: bool
-    user_info: Optional[UserInfo]
+app = FastAPI(
+    title="Dooris", summary="API for interacting with HomeMatic door locks in CCCHH", docs_url="/api/docs",
+    lifespan=lifespan,
+)
 
 
 @app.get("/api/user-info/")
@@ -36,20 +35,43 @@ async def get_user_info() -> UserStatus:
     return { "bla": "blub" }
 
 
-@app.get("/auth/login")
-async def login_init(req: Request):
+@app.get("/auth/login", response_class=RedirectResponse)
+async def login_init(req: Request, resp: Response, next: Optional[str] = "") -> str:
+    # save the ?next url for later redirection if the user requested that
+    if next:
+        resp.set_cookie("auth_next", next, max_age=60 * 10, httponly=True, secure=True, samesite="strict")
+
+    # save the login state into a cookie to prevent CSRF attacks
+    # ref: https://simple-openid-connect.readthedocs.io/en/stable/nonce_and_state.html
+    state = secrets.token_urlsafe(32)
+    resp.set_cookie("auth_state", state, max_age=60 * 10, httponly=True, secure=True, samesite="strict")
+
+    # prevent replay attacks by generating and specifying a nonce
+    # ref: https://simple-openid-connect.readthedocs.io/en/stable/nonce_and_state.html
+    nonce = secrets.token_urlsafe(32)
+    
+    # assemble the response
     oidc_client = req.app.extra["oidc_client"] # type: OpenidClient
-    return RedirectResponse(oidc_client.authorization_code_flow.start_authentication())
+    resp.set_cookie("auth_nonce", nonce, max_age=60*10, httponly=True, secure=True, samesite="strict")
+
+    return oidc_client.authorization_code_flow.start_authentication(state=state, nonce=nonce)
+
 
 
 @app.get("/auth/login-callback")
 async def login_callback(req: Request, resp: Response):
+    if "auth_state" not in req.cookies or "auth_nonce" not in req.cookies:
+        raise ValueError("user is currently not authentication or the authentication expired. try again")
+    
     oidc_client = req.app.extra["oidc_client"] # type: OpenidClient
-    auth_result = oidc_client.authorization_code_flow.handle_authentication_result(current_url=req.url)
+    auth_result = oidc_client.authorization_code_flow.handle_authentication_result(current_url=req.url, state=req.cookies["auth_state"])
     if isinstance(auth_result, TokenSuccessResponse):
-        resp.set_cookie("access_token", auth_result.access_token, httponly=True)
-        resp.set_cookie("id_token", auth_result.id_token)
+        # extract the ID token once now to validate its authenticity
+        _id_token = oidc_client.decode_id_token(auth_result.id_token, nonce=req.cookies["auth_nonce"])
+        
+        resp.set_cookie("access_token", auth_result.access_token, httponly=True, secure=True, samesite="strict")
+        resp.set_cookie("id_token", auth_result.id_token, httponly=False, secure=True, samesite="strict")
         return {"authenticated": True}
     else:
-        return {"authenticated": False}
+        return {"authenticated": False, "error": auth_result}
 

api/src/dooris_api/models.py

@@ -0,0 +1,11 @@
+from typing import Optional
+from pydantic import BaseModel
+
+class UserInfo(BaseModel):
+    name: str
+
+
+class UserStatus(BaseModel):
+    is_logged_in: bool
+    user_info: Optional[UserInfo]
+