crypto: add property for private_key

passbook/crypto/models.py

@@ -4,6 +4,8 @@ from typing import Optional
 
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives import hashes
+from cryptography.hazmat.primitives.asymmetric.rsa import RSAPrivateKey
+from cryptography.hazmat.primitives.serialization import load_pem_private_key
 from cryptography.x509 import Certificate, load_pem_x509_certificate
 from django.db import models
 from django.utils.translation import gettext_lazy as _
@@ -26,6 +28,7 @@ class CertificateKeyPair(UUIDModel, CreatedUpdatedModel):
     )
 
     _cert: Optional[Certificate] = None
+    _key: Optional[RSAPrivateKey] = None
 
     @property
     def certificate(self) -> Certificate:
@@ -36,6 +39,17 @@ class CertificateKeyPair(UUIDModel, CreatedUpdatedModel):
             )
         return self._cert
 
+    @property
+    def private_key(self) -> Optional[RSAPrivateKey]:
+        """Get python cryptography PrivateKey instance"""
+        if not self._key:
+            self._key = load_pem_private_key(
+                str.encode("\n".join([x.strip() for x in self.key_data.split("\n")])),
+                password=None,
+                backend=default_backend(),
+            )
+        return self._key
+
     @property
     def fingerprint(self) -> str:
         """Get SHA256 Fingerprint of certificate_data"""