First attempt at adding support for attribute certificates (#117)

Platform certificates are defined as RFC5755 attribute certificates with
various additional attributes and extensions defined in the TCG Platform
Certificate Profile. Add support for parsing them, derived from
crypto/x509. Include some test certificates and verify we parse them.

attributecert/attributecert_test.go

@@ -0,0 +1,55 @@
+// Copyright 2019 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+package attributecert
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"strings"
+	"testing"
+)
+
+func TestParseAttributeCerts(t *testing.T) {
+	files, err := ioutil.ReadDir("testdata")
+	if err != nil {
+		t.Fatalf("failed to read test dir: %v", err)
+	}
+	for _, file := range files {
+		if strings.HasSuffix(file.Name(), ".json") {
+			continue
+		}
+		filename := "testdata/" + file.Name()
+		jsonfile := filename + ".json"
+		data, err := ioutil.ReadFile(filename)
+		if err != nil {
+			t.Fatalf("failed to read test data %s: %v", filename, err)
+		}
+		cert, err := ParseAttributeCertificate(data)
+		if err != nil {
+			t.Fatalf("failed to parse test data %s: %v", filename, err)
+		}
+		jsondata, err := ioutil.ReadFile(jsonfile)
+		if err != nil {
+			t.Fatalf("failed to read json test data %s: %v", jsonfile, err)
+		}
+		jsoncert, err := json.MarshalIndent(cert, "", "    ")
+		if err != nil {
+			t.Fatalf("failed to marshal %s to json: %v", filename, err)
+		}
+		if string(jsondata) != string(jsoncert) {
+			t.Fatalf("%s fails to match test data", filename)
+		}
+	}
+}