fix(sauce): sauceAgent passed incorrectly to sauce node module

closes #3410

Author: cnishina

lib/config.ts

@@ -93,9 +93,23 @@ export interface Config {
   sauceKey?: string;
   /**
    * Use sauceAgent if you need customize agent for https connection to
-   * saucelabs.com (i.e. your computer behind corporate proxy)
+   * saucelabs.com (i.e. your computer behind corporate proxy).
+   *
+   * To match sauce agent implementation, use
+   * [HttpProxyAgent](https://github.com/TooTallNate/node-http-proxy-agent)
+   * to generate the agent or use sauceProxy as an alternative where
+   * sauce generates the agent for you based on the proxy. If a sauceProxy is
+   * provided, the sauceAgent will be overridden.
+   */
+  sauceAgent?: HttpProxyAgent;
+  /**
+   * Use sauceProxy that will get generated into an agent for https connection
+   * to saucelabs.com (i.e. your computer behind corporate proxy).
+   *
+   * The sauceProxy is used to generate a sauceAgent. If a sauceProxy is
+   * provided, the sauceAgent will be overridden.
    */
-  sauceAgent?: string;
+  sauceProxy?: string;
   /**
    * Use sauceBuild if you want to group test capabilites by a build ID
    */

lib/driverProviders/sauce.ts

@@ -57,7 +57,8 @@ export class Sauce extends DriverProvider {
     this.sauceServer_ = new SauceLabs({
       username: this.config_.sauceUser,
       password: this.config_.sauceKey,
-      agent: this.config_.sauceAgent
+      agent: this.config_.sauceAgent,
+      proxy: this.config_.sauceProxy
     });
     this.config_.capabilities['username'] = this.config_.sauceUser;
     this.config_.capabilities['accessKey'] = this.config_.sauceKey;

lib/globals.d.ts

@@ -105,3 +105,7 @@ declare namespace webdriver {
     isPresent?: Function;
   }
 }
+
+declare interface HttpProxyAgent {
+  constructor(opts: Object): HttpProxyAgent;
+}