adding support to pass Env param to webpack

src/Microsoft.AspNetCore.SpaServices/Webpack/WebpackDevMiddlewareOptions.cs

@@ -50,5 +50,10 @@ namespace Microsoft.AspNetCore.SpaServices.Webpack
         /// the webpack compiler.
         /// </summary>
         public IDictionary<string, string> EnvironmentVariables { get; set; }
+
+        /// <summary>
+        /// Pass in the env parameter to webpack.
+        /// </summary>
+        public object EnvParam { get; set; }
     }
 }

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-webpack/src/WebpackDevMiddleware.ts

@@ -32,6 +32,7 @@ interface DevServerOptions {
     HotModuleReplacementServerPort: number;
     HotModuleReplacementClientOptions: StringMap<string>;
     ReactHotModuleReplacement: boolean;
+    EnvParam: any;
 }
 
 // We support these three kinds of webpack.config.js export. We don't currently support exported promises
@@ -248,7 +249,7 @@ export function createWebpackDevServer(callback: CreateDevServerCallback, option
         // In the future, we could add support for configuring the 'env' param in Startup.cs. But right
         // now, it's not clear that people will want to do that (and they can always make up their own
         // default env values in their webpack.config.js).
-        webpackConfigExport = webpackConfigExport();
+        webpackConfigExport = webpackConfigExport(options.suppliedOptions.EnvParam);
     }
     const webpackConfigArray = webpackConfigExport instanceof Array ? webpackConfigExport : [webpackConfigExport];