Stackdriver - Ability to configure credentials

implementations/micrometer-registry-stackdriver/src/main/java/io/micrometer/stackdriver/StackdriverConfig.java

@@ -15,9 +15,16 @@
  */
 package io.micrometer.stackdriver;
 
+import com.google.api.gax.core.CredentialsProvider;
+import com.google.api.gax.core.FixedCredentialsProvider;
+import com.google.auth.oauth2.GoogleCredentials;
+import com.google.cloud.monitoring.v3.MetricServiceSettings;
 import io.micrometer.core.instrument.config.MissingRequiredConfigurationException;
 import io.micrometer.core.instrument.step.StepRegistryConfig;
 
+import java.io.FileInputStream;
+import java.io.IOException;
+
 /**
  * {@link StepRegistryConfig} for Stackdriver.
  *
@@ -42,4 +49,11 @@ default String resourceType() {
         String resourceType = get(prefix() + ".resourceType");
         return resourceType == null ? "global" : resourceType;
     }
+
+    default CredentialsProvider credentials() throws IOException {
+        String credentials = get(prefix() + ".credentials");
+        return credentials == null ? MetricServiceSettings.defaultCredentialsProviderBuilder().build()
+                : FixedCredentialsProvider.create(GoogleCredentials.fromStream(new FileInputStream(credentials))
+                        .createScoped(MetricServiceSettings.getDefaultServiceScopes()));
+    }
 }

implementations/micrometer-registry-stackdriver/src/main/java/io/micrometer/stackdriver/StackdriverMeterRegistry.java

@@ -85,8 +85,8 @@ public class StackdriverMeterRegistry extends StepMeterRegistry {
     @Nullable
     private MetricServiceClient client;
 
-    public StackdriverMeterRegistry(StackdriverConfig config, Clock clock) {
-        this(config, clock, DEFAULT_THREAD_FACTORY, () -> MetricServiceSettings.newBuilder().build());
+    protected StackdriverMeterRegistry(StackdriverConfig config, Clock clock) {
+        this(config, clock, DEFAULT_THREAD_FACTORY, () ->  MetricServiceSettings.newBuilder().build());
     }
 
     private StackdriverMeterRegistry(StackdriverConfig config, Clock clock, ThreadFactory threadFactory,
@@ -256,6 +256,14 @@ public static class Builder {
 
         Builder(StackdriverConfig config) {
             this.config = config;
+            this.metricServiceSettings = () -> {
+                MetricServiceSettings.Builder builder = MetricServiceSettings.newBuilder();
+                if (config.credentials() != null) {
+                    builder.setCredentialsProvider(config.credentials());
+                }
+                builder.setHeaderProvider(new UserAgentHeaderProvider("stackdriver"));
+                return builder.build();
+            };
         }
 
         public Builder clock(Clock clock) {

implementations/micrometer-registry-stackdriver/src/main/java/io/micrometer/stackdriver/UserAgentHeaderProvider.java

@@ -0,0 +1,74 @@
+/**
+ * Copyright 2019 Pivotal Software, Inc.
+ * <p>
+ * 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
+ * <p>
+ * https://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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 io.micrometer.stackdriver;
+
+import com.google.api.gax.rpc.HeaderProvider;
+
+import java.util.Collections;
+import java.util.Map;
+
+/**
+ * Provides the User-Agent header to signal to the Google Cloud Client Libraries that requests originate from a
+ * Micrometer Stackdriver Registry.
+ *
+ * @author João André Martins
+ * @author Chengyuan Zhao
+ * @author Mike Eltsufin
+ * @author Ray Tsang
+ */
+public class UserAgentHeaderProvider implements HeaderProvider {
+
+    private String userAgent;
+
+    private final Map<String, String> headers;
+
+    /**
+     * Default constructor.
+     *
+     * @param component The component
+     */
+    public UserAgentHeaderProvider(String component) {
+        this.userAgent = computeUserAgent(component);
+        this.headers = Collections.singletonMap("User-Agent", this.userAgent);
+    }
+
+    /**
+     * Returns the "User-Agent" header whose value should be added to the google-cloud-java REST API calls.
+     * e.g., {@code User-Agent: Micrometer/1.0.0.RELEASE micrometer-registry-stackdriver/1.0.0.RELEASE}.
+     */
+    @Override
+    public Map<String, String> getHeaders() {
+        return this.headers;
+    }
+
+    /**
+     * Returns the "User-Agent" header value which should be added to the google-cloud-java calls.
+     * e.g., {@code Micrometer/1.0.0.RELEASE micrometer-registry-stackdriver/1.0.0.RELEASE}.
+     *
+     * @return the user agent string.
+     */
+    public String getUserAgent() {
+        return this.userAgent;
+    }
+
+    private String computeUserAgent(String component) {
+        String library = "micrometer-registry-" + component;
+        String version = this.getClass().getPackage().getImplementationVersion();
+
+        return "Micrometer/" + version + " " + library + "/" + version;
+
+    }
+}