[models] Coerce x509 subject fields to strings

This change allows subclasses to redefine the following
fields as foreign keys without losing compatibility:
- country_code
- state
- city
- organization
- email
- common_name

django_x509/base/models.py

@@ -10,6 +10,7 @@
 from jsonfield import JSONField
 from model_utils.fields import AutoCreatedField, AutoLastModifiedField
 from OpenSSL import crypto
+from six import string_types
 
 from .. import settings as app_settings
 from ..utils import bytes_compat
@@ -220,6 +221,10 @@ def _fill_subject(self, subject):
         for model_attr, subject_attr in attr_map.items():
             value = getattr(self, model_attr)
             if value:
+                # coerce value to string, allow these fields to be redefined
+                # as foreign keys by subclasses without losing compatibility
+                if not isinstance(value, string_types):
+                    value = str(value)
                 setattr(subject, subject_attr, value)
         return subject
 

django_x509/tests/test_ca.py

@@ -15,14 +15,14 @@ class TestCa(TestCase):
     """
     tests for Ca model
     """
-    def _create_ca(self, ext=[]):
-        ca = Ca(name='newcert',
+    def _create_ca(self, organization='OpenWISP', ext=[]):
+        ca = Ca(name='Test CA',
                 key_length='2048',
                 digest='sha256',
                 country_code='IT',
                 state='RM',
                 city='Rome',
-                organization='OpenWISP',
+                organization=organization,
                 email='test@test.com',
                 common_name='openwisp.org',
                 extensions=ext)
@@ -413,3 +413,10 @@ def test_x509_import_exception_fixed(self):
         ca.full_clean()
         ca.save()
         self.assertEqual(ca.email, '')
+
+    def test_fill_subject_non_strings(self):
+        ca1 = self._create_ca()
+        ca2 = Ca(name='ca', organization=ca1)
+        x509 = crypto.X509()
+        subject = ca2._fill_subject(x509.get_subject())
+        self.assertEqual(subject.organizationName, 'Test CA')