+ helper to create CASAccounts for existing users

authens/backends.py

@@ -2,7 +2,7 @@ from django.contrib.auth import get_user_model
 from django.db import transaction
 
 from authens.models import CASAccount, OldCASAccount
-from authens.utils import get_cas_client
+from authens.utils import get_cas_client, parse_entrance_year
 
 UserModel = get_user_model()
 
@@ -11,30 +11,6 @@ class ENSCASError(Exception):
     pass
 
 
-def get_entrance_year(attributes):
-    """Infer the entrance year of a CAS account holder from her home directory."""
-
-    # The home directory of a user is of the form /users/YEAR/DEPARTMENT/CAS_LOGIN where
-    # YEAR is a 2-digit number representing the entrance year of the student. We get the
-    # entrance year from there.
-
-    home_dir = attributes.get("homeDirectory")
-    if home_dir is None:
-        raise ENSCASError("Entrance year not available")
-
-    dirs = home_dir.split("/")
-    if len(dirs) < 3 or not dirs[2].isdecimal():
-        raise ENSCASError("Invalid homeDirectory: {}".format(home_dir))
-
-    # Expand the 2-digit entrance year into 4 digits.
-    # This will break in 2080.
-    year = int(dirs[2])
-    if year >= 80:
-        return 1900 + year
-    else:
-        return 2000 + year
-
-
 class ENSCASBackend:
     """AuthENS CAS authentication backend.
 
@@ -106,8 +82,10 @@ class ENSCASBackend:
         - If a matching CAS account exists, retrieve it.
         """
 
-        entrance_year = get_entrance_year(attributes)
-        email = attributes.get("email", None)
+        email = attributes.get("email")
+        entrance_year = parse_entrance_year(attributes.get("homeDirectory"))
+        if entrance_year is None:
+            raise ENSCASError("Entrance year not available")
 
         with transaction.atomic():
             try:

authens/conf.py

@@ -0,0 +1,4 @@
+default_settings = {
+    "LDAP_SERVER_URL": "ldaps://ldap.spi.ens.fr:636",
+    # TODO: CAS_SERVER_URL
+}

authens/shortcuts.py

@@ -0,0 +1,62 @@
+"""Helper functions to get CAS metadata and create CAS accounts."""
+
+# TODO: make the python-ldap dependency optional
+import ldap
+
+from django.conf import settings
+from django.contrib.auth import get_user_model
+
+from authens.conf import default_settings
+from authens.models import CASAccount, OldCASAccount
+from authens.utils import parse_entrance_year
+
+User = get_user_model()
+
+
+def _extract_ldap_info(entry, field):
+    dn, attrs = entry
+    return attrs[field][0].decode("utf-8")
+
+
+def fetch_cas_account(cas_login):
+    """Issue an LDAP connection to retrieve metadata associated to a CAS account."""
+
+    # Don't trust the user! Only accept alphanumeric account names.
+    if not cas_login.isalnum():
+        raise ValueError("Illegal CAS login: {}".format(cas_login))
+
+    ldap_url = getattr(settings, "LDAP_SERVER_URL", default_settings["LDAP_SERVER_URL"])
+    ldap_obj = ldap.initialize(ldap_url)
+    res = ldap_obj.search_s(
+        "dc=spi,dc=ens,dc=fr",
+        ldap.SCOPE_SUBTREE,
+        "(uid={})".format(cas_login),
+        ["uid", "cn", "homeDirectory"],
+    )
+    if not res:
+        return None
+
+    (res,) = res
+    assert _extract_ldap_info(res, "uid") == cas_login
+    return {
+        "cn": _extract_ldap_info(res, "cn"),
+        "entrance_year": parse_entrance_year(_extract_ldap_info(res, "homeDirectory")),
+    }
+
+
+def register_cas_account(user: User, cas_login: str) -> CASAccount:
+    """Register a user as a CAS user and return the newly created CASAccount."""
+
+    if not cas_login:
+        raise ValueError("cas_login must be non-empty")
+    if CASAccount.objects.filter(cas_login=cas_login).exists():
+        raise ValueError("A CAS account named '{}' exists already".format(cas_login))
+    if CASAccount.objects.filter(user=user).exists():
+        raise ValueError("User '{}' already has a CAS account".format(user))
+    if OldCASAccount.objects.filter(user=user).exists():
+        raise ValueError("User '{}' has an old CAS account".format(user))
+
+    entrance_year = fetch_cas_account(cas_login)["entrance_year"]
+    return CASAccount.objects.create(
+        user=user, cas_login=cas_login, entrance_year=entrance_year
+    )

authens/utils.py

@@ -1,3 +1,5 @@
+"""Internal utility functions used by authens."""
+
 from cas import CASClient
 from urllib.parse import urlunparse
 
@@ -11,3 +13,26 @@ def get_cas_client(request):
         ),
         server_url="https://cas.eleves.ens.fr/",
     )
+
+
+def parse_entrance_year(home_dir):
+    """Infer the entrance year of a CAS account from their home directory."""
+
+    # The home directory of a user is of the form /users/YEAR/DEPARTMENT/CAS_LOGIN where
+    # YEAR is a 2-digit number representing the entrance year of the student. We get the
+    # entrance year from there.
+
+    if home_dir is None:
+        return None
+
+    dirs = home_dir.split("/")
+    if len(dirs) < 3 or not dirs[2].isdecimal() or dirs[1] != "users":
+        raise ValueError("Invalid home directory: {}".format(home_dir))
+
+    # Expand the 2-digit entrance year into 4 digits.
+    # This will break in 2080.
+    year = int(dirs[2])
+    if year >= 80:
+        return 1900 + year
+    else:
+        return 2000 + year