content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.beam.sdk.extensions.gcp.auth;
  
  import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
  
  import com.google.auth.Credentials;
  import com.google.auth.oauth2.GoogleCredentials;
  import com.google.auth.oauth2.ImpersonatedCredentials;
  import java.io.IOException;
  import java.util.Arrays;
  import java.util.List;
  import org.apache.beam.sdk.extensions.gcp.options.GcpOptions;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * Construct an oauth credential to be used by the SDK and the SDK workers. Returns a GCP
   * credential.
   */
  public class GcpCredentialFactory implements CredentialFactory {
    // A list of OAuth scopes to request when creating a credential.
    private List<String> oauthScopes;
    // If non-null, a list of service account emails to be used as an impersonation chain.
    private @Nullable List<String> impersonateServiceAccountChain;
  
    private GcpCredentialFactory(
        List<String> oauthScopes, @Nullable List<String> impersonateServiceAccountChain) {
      if (impersonateServiceAccountChain != null) {
        checkArgument(impersonateServiceAccountChain.size() > 0);
      }
  
      this.oauthScopes = oauthScopes;
      this.impersonateServiceAccountChain = impersonateServiceAccountChain;
    }
  
    public static GcpCredentialFactory fromOptions(PipelineOptions options) {
      GcpOptions gcpOptions = options.as(GcpOptions.class);
      @Nullable String impersonateServiceAccountArg = gcpOptions.getImpersonateServiceAccount();
  
      @Nullable
      List<String> impersonateServiceAccountChain =
          impersonateServiceAccountArg == null
              ? null
              : Arrays.asList(impersonateServiceAccountArg.split(","));
  
      return new GcpCredentialFactory(gcpOptions.getGcpOauthScopes(), impersonateServiceAccountChain);
    }
  
    /** Returns a default GCP {@link Credentials} or null when it fails. */
    @Override
    public @Nullable Credentials getCredential() {
      try {
        GoogleCredentials applicationDefaultCredentials =
            GoogleCredentials.getApplicationDefault().createScoped(oauthScopes);
  
        if (impersonateServiceAccountChain == null) {
          return applicationDefaultCredentials;
        } else {
          String targetPrincipal =
              impersonateServiceAccountChain.get(impersonateServiceAccountChain.size() - 1);
          List<String> delegationChain =
              impersonateServiceAccountChain.subList(0, impersonateServiceAccountChain.size() - 1);
  
          GoogleCredentials impersonationCredentials =
              ImpersonatedCredentials.create(
                  applicationDefaultCredentials, targetPrincipal, delegationChain, oauthScopes, 0);
  
          return impersonationCredentials;
        }
      } catch (IOException e) {
        // Ignore the exception
        // Pipelines that only access to public data should be able to run without credentials.
        return null;
      }
    }
  }
  