feat(ldap): create function for user existence check

lumi2/ldap.py

@@ -553,6 +553,32 @@ def create_ou(connection: Connection, ou_dn: str) -> None:
     connection.add(ou_dn, 'organizationalUnit')
 
 
+def user_exists(connection: Connection, user_dn: str) -> bool:
+    """Checks whether the specified user entry exists in the DIT.
+
+    The user DN is expected to represent an entry which is a direct child of the
+    LDAP_USERS_OU specified in the app config.
+
+    Parameters
+    ----------
+    Connection : ldap3.Connection
+        Bound Connection object to an LDAP server.
+    ou_dn : str
+        DN of a user entry (uid) directly below the LDAP_USERS_OU entry.
+
+    Raises
+    ------
+    MissingParentEntryException
+        If the specified user DN's direct parent entry is not present in the DIT.
+    """
+
+    _assert_is_valid_connection(connection)
+    _assert_is_valid_user_dn(user_dn)
+
+    # TODO implement
+    return False
+
+
 def get_user(connection: Connection, uid: str) -> User:
     """Retrieves the user with the specified uid (username) from the LDAP server.