raise on invalid top-level keys in hub.config

jupyterhub/files/hub/jupyterhub_config.py

@@ -478,16 +478,33 @@ def camelCaseify(s):
 c.CryptKeeper.keys = get_secret_value("hub.config.CryptKeeper.keys").split(";")
 
 # load hub.config values, except potentially seeded secrets already loaded
-for app, cfg in get_config("hub.config", {}).items():
-    if app == "JupyterHub":
+for section, cfg in get_config("hub.config", {}).items():
+    if section == "JupyterHub":
         cfg.pop("proxy_auth_token", None)
         cfg.pop("cookie_secret", None)
         cfg.pop("services", None)
-    elif app == "ConfigurableHTTPProxy":
+    elif section == "ConfigurableHTTPProxy":
         cfg.pop("auth_token", None)
-    elif app == "CryptKeeper":
+    elif section == "CryptKeeper":
         cfg.pop("keys", None)
-    c[app].update(cfg)
+
+    if not section[:1].isupper():
+        # traitlets config sections are Configurable class names
+        # that MUST start with upper-case
+        # if it starts with lowercase, it must be a mistake
+        # (e.g. putting `hub.loadRoles` under `hub.config.loadRoles`),
+        # and will have no effect, so warn or raise here
+        print(
+            f"FATAL: Invalid hub.config section name: {section}."
+            " hub.config sections must be Configurable class names (e.g. JupyterHub)."
+            " Maybe misplaced or misspelled config?",
+            file=sys.stderr,
+        )
+        # make this fatal:
+        sys.exit(1)
+
+    print(f"Loading pass-through config section hub.config.{section}")
+    c[section].update(cfg)
 
 # load /usr/local/etc/jupyterhub/jupyterhub_config.d config files
 config_dir = "/usr/local/etc/jupyterhub/jupyterhub_config.d"

jupyterhub/values.schema.yaml

@@ -207,7 +207,7 @@ properties:
           for more info.
       config:
         type: object
-        additionalProperties: true
+        additionalProperties: false
         description: |
           JupyterHub and its components (authenticators, spawners, etc), are
           Python classes that expose its configuration through
@@ -271,6 +271,18 @@ properties:
           the `--values` or `-f` flag. During merging, lists are replaced while
           dictionaries are updated.
           ```
+        # check that the first character is Capital,
+        # which is required for valid section names
+        # can't know all possible Configurable class names in advance, though
+        patternProperties:
+          "^[A-Z].*$":
+            type: object
+            additionalProperties: true
+            description: |
+              Pass-through traitlets configuration of Configurable classes.
+              Keys must always be class names that start with capitals,
+              and values must be objects.
+
         properties:
           JupyterHub:
             type: object