Made PKCE and nonce optional, only when client wants them.

paskia/authcode.py

@@ -23,15 +23,15 @@ AUTH_CODE_LIFETIME = timedelta(seconds=60)
 class OIDCCode(msgspec.Struct):
     """An OIDC authorization code pending token exchange.
 
-    PKCE uses S256 only (verified at auth time).
+    PKCE uses S256 only when provided (verified at token exchange).
     """
 
     session_key: str
     created: datetime
     redirect_uri: str
     scope: str
-    nonce: str
-    code_challenge: str
+    nonce: str | None = None
+    code_challenge: str | None = None
 
 
 class CookieCode(msgspec.Struct):

paskia/fastapi/oid.py

@@ -196,7 +196,8 @@ async def _handle_authorization_code(
             status_code=400,
         )
 
-    # Verify PKCE (S256 only, enforced at auth time)
+    # Verify PKCE if code_challenge was provided at authorization time
+    if oidc_code.code_challenge:
         if not code_verifier:
             return JSONResponse(
                 {

paskia/fastapi/ws.py

@@ -158,12 +158,10 @@ async def websocket_authenticate(
             await ws.send_json({"status": 400, "detail": "Scope must include openid"})
             return
 
-        # PKCE is required with S256
-        if not code_challenge:
-            await ws.send_json(
-                {"status": 400, "detail": "PKCE code_challenge is required"}
-            )
-            return
+        # PKCE: when code_challenge is present, only S256 is supported
+        # If method is omitted, default to S256 per best practice (not "plain" per RFC 7636)
+        # When code_challenge is absent, ignore code_challenge_method entirely
+        if code_challenge:
             if code_challenge_method and code_challenge_method != "S256":
                 await ws.send_json(
                     {
@@ -172,11 +170,7 @@ async def websocket_authenticate(
                     }
                 )
                 return
-
-        # Nonce is required for OIDC
-        if not nonce:
-            await ws.send_json({"status": 400, "detail": "nonce is required for OIDC"})
-            return
+            # Default to S256 when method not specified (implicit)
 
         # Validate state parameter if provided (defensive against injection)
         if state: