feat(auth): create a zero-OID for Subject Public Key

Created an explicit zero-OID which can be used for Subject
Public Key that do not have their own key identifier.

With this, all keys (including the subject public key) have
a proper key OID string so we don't need to make a special
case of null pointers when it comes to handling key OIDs.

Change-Id: Ice6923951699b6e253d7fd87e4c1b912470e0391
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>

include/tools_share/cca_oid.h

@@ -9,6 +9,7 @@
 
 /* Reuse the Object IDs defined by TBBR for certificate extensions. */
 #include "tbbr_oid.h"
+#include "zero_oid.h"
 
 /*
  * Assign arbitrary Object ID values that do not conflict with any of the

include/tools_share/dualroot_oid.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Arm Limited. All rights reserved.
+ * Copyright (c) 2020-2023, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,6 +9,7 @@
 
 /* Reuse the Object IDs defined by TBBR for certificate extensions. */
 #include "tbbr_oid.h"
+#include "zero_oid.h"
 
 /*
  * Platform root-of-trust public key.

include/tools_share/zero_oid.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2023, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef ZERO_OID_H
+#define ZERO_OID_H
+
+#define ZERO_OID                              "0.0.0.0.0.0.0.0.0"
+
+#endif /* ZERO_OID_H */