the LAN rule moves from nginx into the app, as a setting for keys only

api_keys_from is a typed setting, lan (default, the historical rule) or
anywhere, checked in admin_api._auth against the first X-Forwarded-For hop
that NPM sets. It governs API keys only: a session is never restricted, the
console is a session from anywhere; and the break-glass token is ALWAYS
LAN-only, which is not a choice and so is not a setting. LAN ranges are
facts about the network and live in code; the docker range is included
because NPM, the routines and sibling containers reach the app from
arrstack_arr_net. An unparseable address is not LAN - the rule fails closed.

With this in place the location /api/admin/ block on NPM host 51 can come
out; the app enforces what it enforced, and the toggle never touches NPM.

tests/smoke_admin.py 58 -> 76. Proven on a throwaway site: key LAN 200,
key WAN 403 naming the setting, session WAN 200, token LAN 200, token WAN
403; set anywhere, key WAN 200 and token WAN still 403; bogus value 422.

app/admin_api.py

@@ -40,6 +40,7 @@ one CAPS dictionary - never by a role comparison here.
 import hmac
 import html as _html
 import inspect
+import ipaddress
 import os
 import re
 
@@ -60,6 +61,26 @@ router = APIRouter(prefix="/api/admin", tags=["admin"])
 docs_router = APIRouter(prefix="/api", tags=["docs"])
 
 
+# What counts as "inside" for the LAN rule. Facts about the network, so
+# they live in code; the CHOICE of whether keys are LAN-only is a setting.
+# The docker range is here because NPM, the routines and any sibling
+# container reach this app from arrstack_arr_net, and a container on that
+# network is already inside.
+LAN_NETS = [ipaddress.ip_network(n) for n in
+            ("10.0.0.0/24", "10.0.1.0/24", "127.0.0.0/8", "172.16.0.0/12")]
+
+
+def client_is_lan(request):
+    """True if the caller's address is on the LAN. Uses the first
+    X-Forwarded-For hop, which NPM sets; an unparseable or absent address is
+    NOT lan - the rule fails closed."""
+    try:
+        ip = ipaddress.ip_address(auth._client_ip(request) or "")
+    except ValueError:
+        return False
+    return any(ip in n for n in LAN_NETS)
+
+
 def _person(request):
     """Who is calling: a session first, then an API key, then nobody.
 
@@ -89,6 +110,10 @@ def _auth(request, token, capability, unit_id=None):
     """
     person = _person(request)
     if person:
+        if person.get("key_scopes") is not None and not client_is_lan(request) \
+                and identity.get_setting("api_keys_from") == "lan":
+            raise HTTPException(403, "API keys may only be used from the LAN right now "
+                                     "(site setting api_keys_from)")
         if not identity.can(person, capability, unit_id):
             raise HTTPException(403, "your account does not have %s" % capability
                                 + (" for this unit" if unit_id else "")
@@ -99,6 +124,10 @@ def _auth(request, token, capability, unit_id=None):
         raise HTTPException(503, "admin API disabled: sign in, or set ADMIN_TOKEN")
     if not token or not hmac.compare_digest(token, ADMIN_TOKEN):
         raise HTTPException(401, "sign in, or send a valid X-Admin-Token")
+    # The shared token is break glass for an operator at the console. It is
+    # never usable from outside, and that is not a setting.
+    if not client_is_lan(request):
+        raise HTTPException(403, "the admin token is LAN-only")
     return "admin-token"
 
 
@@ -380,13 +409,19 @@ def whoami(request: Request, x_admin_token: str = Header(None)):
     call with a new key."""
     person = _person(request)
     if person:
+        if person.get("key_scopes") is not None and not client_is_lan(request) \
+                and identity.get_setting("api_keys_from") == "lan":
+            raise HTTPException(403, "API keys may only be used from the LAN right now "
+                                     "(site setting api_keys_from)")
         return {"email": person["email"], "global_role": person.get("global_role"),
-                "capabilities": person["capabilities"],
+                "capabilities": person["capabilities"], "lan": client_is_lan(request),
                 "via": ("key " + person["key_prefix"]) if person.get("key_scopes") is not None else "session"}
     if not ADMIN_TOKEN:
         raise HTTPException(503, "admin API disabled: sign in, or set ADMIN_TOKEN")
     if x_admin_token and hmac.compare_digest(x_admin_token, ADMIN_TOKEN):
-        return {"email": None, "via": "admin-token", "capabilities": ["*"]}
+        if not client_is_lan(request):
+            raise HTTPException(403, "the admin token is LAN-only")
+        return {"email": None, "via": "admin-token", "capabilities": ["*"], "lan": True}
     raise HTTPException(401, "sign in, send a Bearer key, or a valid X-Admin-Token")