Add tests for keyUsage to the built-in cert verifier.

net/data/verify_certificate_chain_unittest/generate-serverauth-rsa-ku-keyagreement.py

+#!/usr/bin/python
+# Copyright (c) 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Certificate chain with 1 intermediate, a trusted root, and a target
+certificate for serverAuth that has only keyAgreement."""
+
+import common
+
+# Self-signed root certificate (used as trust anchor).
+root = common.create_self_signed_root_certificate('Root')
+
+# Intermediate certificate.
+intermediate = common.create_intermediate_certificate('Intermediate', root)
+
+# Target certificate.
+target = common.create_end_entity_certificate('Target', intermediate)
+target.set_key(common.get_or_generate_rsa_key(
+    2048, common.create_key_path(target.name)))
+target.get_extensions().set_property('extendedKeyUsage', 'serverAuth')
+target.get_extensions().set_property('keyUsage', 'critical,keyAgreement')
+
+
+chain = [target, intermediate]
+trusted = common.TrustAnchor(root, constrained=False)
+time = common.DEFAULT_TIME
+key_purpose = common.KEY_PURPOSE_SERVER_AUTH
+verify_result = True
+errors = None
+
+common.write_test_file(__doc__, chain, trusted, time, key_purpose,
+                       verify_result, errors)