Add auth support for gRPC (#323)

* Add auth support for gRPC

* Add comment on static headers

* Update examples/otlptrace/src/main/java/com/google/cloud/opentelemetry/example/otlptrace/OTLPTraceExample.java

Co-authored-by: David Ashpole <dashpole@google.com>

---------

Co-authored-by: David Ashpole <dashpole@google.com>

Author: psx95

examples/otlptrace/README.md

@@ -22,6 +22,8 @@ Next, update [`build.gradle`](build.grade) to set the following:
 ```
 	'-Dotel.resource.attributes=gcp.project_id=<YOUR_PROJECT_ID>,
 	'-Dotel.exporter.otlp.headers=X-Goog-User-Project=<YOUR_QUOTA_PROJECT>',
+	# Optional - if you want to export using gRPC protocol
+	'-Dotel.exporter.otlp.protocol=grpc',
 ```
 
 Finally, to run the sample from the project root:

examples/otlptrace/src/main/java/com/google/cloud/opentelemetry/example/otlptrace/OTLPTraceExample.java

@@ -20,11 +20,12 @@
 import io.opentelemetry.context.Scope;
 import io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporter;
 import io.opentelemetry.exporter.otlp.http.trace.OtlpHttpSpanExporterBuilder;
+import io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporter;
+import io.opentelemetry.exporter.otlp.trace.OtlpGrpcSpanExporterBuilder;
 import io.opentelemetry.sdk.OpenTelemetrySdk;
 import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;
 import io.opentelemetry.sdk.common.CompletableResultCode;
 import io.opentelemetry.sdk.trace.export.SpanExporter;
-import java.io.*;
 import java.io.IOException;
 import java.util.Random;
 import java.util.concurrent.TimeUnit;
@@ -48,6 +49,8 @@ private static OpenTelemetrySdk setupTraceExporter() throws IOException {
   }
 
   // Modifies the span exporter initially auto-configured using environment variables
+  // Note: This adds static authorization headers which are set only at initialization time.
+  // This will stop working after the token expires, since the token is not refreshed.
   private static SpanExporter addAuthorizationHeaders(
       SpanExporter exporter, GoogleCredentials credentials) {
     if (exporter instanceof OtlpHttpSpanExporter) {
@@ -63,6 +66,18 @@ private static SpanExporter addAuthorizationHeaders(
       } catch (IOException e) {
         System.out.println("error:" + e.getMessage());
       }
+    } else if (exporter instanceof OtlpGrpcSpanExporter) {
+      try {
+        credentials.refreshIfExpired();
+        OtlpGrpcSpanExporterBuilder builder =
+            ((OtlpGrpcSpanExporter) exporter)
+                .toBuilder()
+                    .addHeader(
+                        "Authorization", "Bearer " + credentials.getAccessToken().getTokenValue());
+        return builder.build();
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
     }
     return exporter;
   }