const google = require('googleapis');

    function getServiceAccountInfo() {
      return {
        type: 'service_account',
        project_id: 'XXXXX',
        private_key_id: 'XXXXXX',
        private_key: 'XXXX',
        client_email: 'XXXX',
        client_id: 'XXXX',
        auth_uri: 'XXXX',
        token_uri: 'XXXX',
        auth_provider_x509_cert_url: 'XXXX',
        client_x509_cert_url: 'XXXXX'
      };
    }

    const SCOPES = 'https://www.googleapis.com/auth/firebase.messaging';

    let proxy2 = {
      host: 'proxy.hkcsl.net',
      port: 8080
    };

    const proxy3 = {
      proxy: 'http://172.25.2.6:8080'
    }

    const proxy4 = {
      proxy: {
        host: '172.25.2.6',
        port: 8080,
        auth: {
          username: '',
          password: '',
        },
      }
    }

    process.env.HTTPS_PROXY = 'https://172.25.2.6:8080';
    process.env.https_proxy = 'https://172.25.2.6:8080';
    process.env.HTTP_PROXY = 'http://172.25.2.6:8080';
    process.env.http_proxy = 'http://172.25.2.6:8080';
    google.options({
      proxy: proxy4.proxy
    });

    const key = getServiceAccountInfo();
    const jwtClient = new google.auth.JWT(
      key.client_email,
      undefined, // null,
      key.private_key,
      SCOPES,
      undefined, // null
    );
    jwtClient.authorize(function(err, tokens) {
      if (err) {
        console.error(err);
        return;
      }
      console.log(tokens.access_token);
    });