test(infra): medewerker login must be refused without a second factor (refs #132)

The keycloak smoke check now asserts that a password-only grant on the medewerker
realm is rejected and that a TOTP code completes it. The e2e medewerker logins move
to a shared helper that submits Keycloak's OTP challenge. Both fail against the
current realm export, which enforces no MFA.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

infra/keycloak/check_realms.py

@@ -1,19 +1,25 @@
 #!/usr/bin/env python3
 """Smoke-check the Keycloak realms: each realm's OIDC login works (password grant)
-and returns its expected identifying claim. Stdlib only. Exits non-zero on failure.
+and returns its expected identifying claim. The medewerker realm additionally enforces
+MFA (S-15c), so its login must be refused without a TOTP code. Stdlib only.
+Exits non-zero on failure.
 """
-import base64, json, sys, urllib.error, urllib.parse, urllib.request
+import base64, hashlib, hmac, json, struct, sys, time, urllib.error, urllib.parse, urllib.request
 
 BASE = "http://localhost:8180"
 CLIENT = "big-portal"
 PWD = "test123"
 
-# realm, user, claim ("__roles__" => check realm_access.roles), expected-contains
+# Fixture TOTP secret seeded into every medewerker in infra/keycloak/realms/medewerker-realm.json.
+# Keycloak HMACs the raw secret bytes, so no base32 decoding is involved.
+OTP_SECRET = b"BIGMEDEWERKEROTPSEED"
+
+# realm, user, claim ("__roles__" => check realm_access.roles), expected-contains, mfa-enforced
 CHECKS = [
-    ("digid", "jan-burger", "bsn", "123456782"),
-    ("eherkenning", "acme-ondernemer", "kvk", "12345678"),
-    ("eidas", "pierre-dupont", "eidas_id", "FR/NL"),
-    ("medewerker", "merel-behandelaar", "__roles__", "behandelaar"),
+    ("digid", "jan-burger", "bsn", "123456782", False),
+    ("eherkenning", "acme-ondernemer", "kvk", "12345678", False),
+    ("eidas", "pierre-dupont", "eidas_id", "FR/NL", False),
+    ("medewerker", "merel-behandelaar", "__roles__", "behandelaar", True),
 ]
 
 
@@ -23,10 +29,17 @@ def decode(jwt):
     return json.loads(base64.urlsafe_b64decode(p))
 
 
-def grant(realm, user):
+def totp(secret=OTP_SECRET, period=30, digits=6):
+    """RFC 6238 code: HMAC-SHA1 over the 30-second counter, dynamically truncated."""
+    mac = hmac.new(secret, struct.pack(">Q", int(time.time()) // period), hashlib.sha1).digest()
+    o = mac[-1] & 0x0F
+    return str((struct.unpack(">I", mac[o:o + 4])[0] & 0x7FFFFFFF) % 10 ** digits).zfill(digits)
+
+
+def grant(realm, user, **extra):
     data = urllib.parse.urlencode({
         "grant_type": "password", "client_id": CLIENT,
-        "username": user, "password": PWD, "scope": "openid",
+        "username": user, "password": PWD, "scope": "openid", **extra,
     }).encode()
     req = urllib.request.Request(
         f"{BASE}/realms/{realm}/protocol/openid-connect/token", data=data,
@@ -35,11 +48,27 @@ def grant(realm, user):
         return json.loads(r.read())
 
 
+def second_factor_refused(realm, user):
+    """The password alone must not yield a token on an MFA-enforced realm."""
+    try:
+        grant(realm, user)
+    except urllib.error.HTTPError as e:
+        return e.code in (400, 401)
+    return False
+
+
 def main():
     ok = True
-    for realm, user, claim, expect in CHECKS:
+    for realm, user, claim, expect, mfa in CHECKS:
+        extra = {}
+        if mfa:
+            refused = second_factor_refused(realm, user)
+            ok = ok and refused
+            print(f"{realm:12} {user:18} password-only login refused "
+                  f"[{'OK' if refused else 'MFA NOT ENFORCED'}]")
+            extra = {"totp": totp()}
         try:
-            at = decode(grant(realm, user)["access_token"])
+            at = decode(grant(realm, user, **extra)["access_token"])
             if claim == "__roles__":
                 val = at.get("realm_access", {}).get("roles", [])
                 good = expect in val