Cloudprober OAuth: Add support for JWT as access token.

common/oauth/oauth.go

@@ -52,6 +52,14 @@ func TokenSourceFromConfig(c *configpb.Config, l *logger.Logger) (oauth2.TokenSo
 			return nil, fmt.Errorf("error reading Google Credentials file (%s): %v", f, err)
 		}
 
+		aud := c.GetGoogleCredentials().GetAudience()
+		if aud != "" || c.GetGoogleCredentials().GetJwtAsAccessToken() {
+			if !c.GetGoogleCredentials().GetJwtAsAccessToken() {
+				return nil, fmt.Errorf("oauth: audience (%s) should only be set if jwt_as_access_token is set to true", aud)
+			}
+			return google.JWTAccessTokenSourceFromJSON(jsonKey, aud)
+		}
+
 		creds, err := google.CredentialsFromJSON(context.Background(), jsonKey, c.GetGoogleCredentials().GetScope()...)
 		if err != nil {
 			return nil, fmt.Errorf("error parsing Google Credentials file (%s): %v", f, err)

common/oauth/oauth_test.go

@@ -0,0 +1,102 @@
+// 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 oauth
+
+import (
+	"fmt"
+	"io/ioutil"
+	"strings"
+	"testing"
+
+	"github.com/golang/protobuf/proto"
+	configpb "github.com/google/cloudprober/common/oauth/proto"
+)
+
+func createTempFile(t *testing.T, b []byte) string {
+	tmpfile, err := ioutil.TempFile("", "")
+	if err != nil {
+		t.Fatal(err)
+		return ""
+	}
+
+	defer tmpfile.Close()
+	if _, err := tmpfile.Write(b); err != nil {
+		t.Fatal(err)
+	}
+
+	return tmpfile.Name()
+}
+
+var testPrivateKey = `-----BEGIN RSA PRIVATE KEY-----
+MIIBPAIBAAJBAN6ErRPkzBWt+R+kMtbbAgmFal+ZbVoWSJDzsLFwdzfy0QaI6Svq
+g4zpfn/H7lXi5MPJ+OWWhFy2DRD0L01PF8kCAwEAAQJBAM59MF+Vog08NEI4jTT0
+Zx+OvveX2PIQW6anfQAr7XXsEo910bPjb9YdfFaHyQCS8aIYeQ7vXD8tV6Vlu93B
+LkECIQD77dd8JWEZp2ZCt0SpN6mPcNOvVoXhvdKp9SiqMorn0wIhAOIdK5hbx/d+
+rextXrNWAeT2PrWxYN7FX1neuAzebrxzAiEA9b9vuQlZa8XwqdnOX2cNvv+nbt1u
+4eLiMaoVDdkZyMMCIQDRXslbTsEevsI1RiCGVoFyjUEL5K8aGBBumvg5kk1fWQIg
+X5mM0KsPPfa9wLSGj6CPt2c3skhQu/k2FjMASmaQbZw=
+-----END RSA PRIVATE KEY-----`
+
+func testJSONKey() string {
+	keyTmpl := `{
+  "type": "service_account",
+  "project_id": "cloud-nat-prober",
+  "private_key_id": "testprivateid",
+  "private_key": "%s",
+  "client_email": "[email protected]",
+  "client_id": "testclientid",
+  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
+  "token_uri": "https://oauth2.googleapis.com/token",
+  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
+  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/test-consumer%%40test-project.iam.gserviceaccount.com"
+}
+`
+	return fmt.Sprintf(keyTmpl, strings.Replace(testPrivateKey, "\n", "\\n", -1))
+}
+
+func TestGoogleCredentials(t *testing.T) {
+	jsonF := createTempFile(t, []byte(testJSONKey()))
+
+	googleC := &configpb.GoogleCredentials{
+		JsonFile: proto.String(jsonF),
+	}
+
+	c := &configpb.Config{
+		Type: &configpb.Config_GoogleCredentials{
+			GoogleCredentials: googleC,
+		},
+	}
+
+	_, err := TokenSourceFromConfig(c, nil)
+	if err != nil {
+		t.Errorf("Config: %v, Unexpected error: %v", c, err)
+	}
+
+	// Set audience, it should fail as jwt_as_access_token is not set.
+	googleC.Audience = proto.String("test-audience")
+
+	_, err = TokenSourceFromConfig(c, nil)
+	if err == nil {
+		t.Errorf("Config: %v, Expected error, but got none.", c)
+	}
+
+	// Set jwt_as_access_token, no errors now.
+	googleC.JwtAsAccessToken = proto.Bool(true)
+
+	_, err = TokenSourceFromConfig(c, nil)
+	if err != nil {
+		t.Errorf("Config: %v, Unexpected error: %v", c, err)
+	}
+}

common/oauth/proto/config.proto

@@ -35,4 +35,11 @@ message BearerToken {
 message GoogleCredentials {
   optional string json_file = 1;
   repeated string scope = 2;
+
+  // Use encoded JWT directly as access token, instead of implementing the whole
+  // OAuth2.0 flow.
+  optional bool jwt_as_access_token = 4;
+
+  // Audience works only if jwt_as_access_token is true.
+  optional string audience = 3;
 }