Adding support for the Certificate managed object

This change polishes and reorganizes the implementation of the
Certificate managed object and its required subclasses. It adds in
documentation and test suites for all modified classes and updates the
SecretFactory to support creating default Certificate objects.

kmip/core/misc.py

@@ -17,6 +17,7 @@ from kmip.core.enums import KeyFormatType as KeyFormatTypeEnum
 from kmip.core.enums import Tags
 from kmip.core.enums import QueryFunction as QueryFunctionEnum
 
+from kmip.core.primitives import ByteString
 from kmip.core.primitives import Enumeration
 from kmip.core.primitives import Interval
 from kmip.core.primitives import Struct
@@ -25,6 +26,27 @@ from kmip.core.primitives import TextString
 from kmip.core.utils import BytearrayStream
 
 
+class CertificateValue(ByteString):
+    """
+    The bytes of a DER-encoded X.509 public key certificate.
+
+    Used by the Certificate Managed Object to store the bytes of the
+    certificate. See Section 2.2.1 of the KMIP 1.1. specification for more
+    information.
+    """
+
+    def __init__(self, value=b''):
+        """
+        Construct a CertificateValue byte string.
+
+        Args:
+            value (bytes): A byte string (e.g., b'\x00\x01...') containing the
+                certificate bytes to store. Optional, defaults to the empty
+                byte string.
+        """
+        super(CertificateValue, self).__init__(value, Tags.CERTIFICATE_VALUE)
+
+
 class Offset(Interval):
     """
     An integer representing a positive change in time.