python: add KeyCredentialLinkDn BinaryDn subtype

This works as a BinaryDn, but it also does validation to ensure the
binary contains a KEYCREDENTIALLINK_BLOB.

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>

diff --git a/python/samba/key_credential_link.py b/python/samba/key_credential_link.py
new file mode 100644 (file)
index 0000000..5371f8b
--- /dev/null
+++ b/python/samba/key_credential_link.py
@@ -0,0 +1,56 @@
+# Unix SMB/CIFS implementation.
+# Copyright (C) Catalyst.Net Ltd 2025
+#
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+#
+
+"""Functions for processing key_credential_link"""
+
+
+from samba.samdb import BinaryDn
+from samba.ndr import ndr_unpack, ndr_pack
+from samba.dcerpc import keycredlink
+
+
+class KeyCredentialLinkDn(BinaryDn):
+    """KeyCredentialLink attributes are stored as DN+Binary.
+
+    The binary part is a KEYCREDENTIALLINK_BLOB, which is basically an
+    array of KEYCREDENTIALLINK_ENTRY collectively describing a public
+    key.
+
+    Usually the DN refers to the object the KeyCredentialLink was
+    found on.
+    """
+    # We make .binary a @property, so that BinaryDn's .parse() and
+    # .prefix just work without knowing that assigning to .binary is
+    # doing validation checks.
+    blob = None
+
+    @property
+    def binary(self) -> bytes:
+        """The binary is stored as a keycredlink.KEYCREDENTIALLINK_BLOB"""
+        if self.blob is None:
+            return None
+        return ndr_pack(self.blob)
+
+    @binary.setter
+    def binary(self, value:bytes):
+        try:
+            self.blob = ndr_unpack(keycredlink.KEYCREDENTIALLINK_BLOB,
+                                   value)
+        except Exception as e:
+            raise ValueError("Could not parse value as KEYCREDENTIALLINK_BLOB "
+                             f" (internal error: {e})")