使用powershell将具有多个值的元素添加到现有xml文件

我正在自动化SQL Reporting Services，我需要将代理设置添加到web.config文件中。我尝试在Powershell中执行此操作，但是我无法弄清楚如何通过Powershell进行此操作。

我需要在现有的web.config XML文件的末尾添加以下xml代码

  <system.net>
    <defaultProxy enabled="true" useDefaultCredentials="true">
      <proxy bypassonlocal="True" proxyaddress="http://ocs.kennisnet.nl:3128" />
    </defaultProxy>
  </system.net>

完整的xml文件需要为：

<configuration>
  <system.web>
    <pages validateRequest="false">
      <controls>
        <add tagPrefix="asp" namespace="System.Web.UI" assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </controls>
      <namespaces>
        <remove namespace="System.Linq" />
        <remove namespace="System.ComponentModel.DataAnnotations" />
      </namespaces>
    </pages>
    <authentication mode="Windows" />
    <identity impersonate="true" />
    <compilation defaultLanguage="c#" debug="false" targetFramework="4.0" tempDirectory="E:\Program Files\Microsoft SQL Server Reporting Services\SSRS\ReportServer\RSTempFiles">
      <assemblies>
        <clear />
        <add assembly="ReportingServicesWebServer" />
        <add assembly="System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
        <add assembly="System.Web.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
        <add assembly="System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
        <add assembly="System.Xml.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
        <add assembly="System.Web.DynamicData, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      </assemblies>
    </compilation>
    <trace enabled="false" requestLimit="10" pageOutput="false" traceMode="SortByTime" localOnly="true" />
    <sessionState mode="Off" />
    <httpHandlers>
      <add verb="*" path="Reserved.ReportServer" type="Microsoft.ReportingServices.WebServer.ReportServiceHttpHandler, ReportingServicesWebServer" />
      <add verb="*" path="Reserved.ReportViewerWebControl.axd" type="Microsoft.Reporting.WebForms.HttpHandler, ReportingServicesWebServer, Version=14.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91" />
      <add verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" validate="false" />
    </httpHandlers>
    <httpModules>
      <clear />
      <add name="OutputCache" type="System.Web.Caching.OutputCacheModule" />
      <add name="WindowsAuthentication" type="System.Web.Security.WindowsAuthenticationModule" />
      <add name="FormsAuthentication" type="System.Web.Security.FormsAuthenticationModule" />
      <add name="PassportAuthentication" type="System.Web.Security.PassportAuthenticationModule" />
      <add name="RoleManager" type="System.Web.Security.RoleManagerModule" />
      <add name="UrlAuthorization" type="System.Web.Security.UrlAuthorizationModule" />
      <add name="FileAuthorization" type="System.Web.Security.FileAuthorizationModule" />
      <add name="AnonymousIdentification" type="System.Web.Security.AnonymousIdentificationModule" />
      <add name="Profile" type="System.Web.Profile.ProfileModule" />
      <add name="ErrorHandlerModule" type="System.Web.Mobile.ErrorHandlerModule, System.Web.Mobile, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
    </httpModules>
    <globalization requestEncoding="utf-8" responseEncoding="utf-8" />
    <httpRuntime executionTimeout="9000" requestValidationMode="2.0" />
    <securityPolicy>
      <trustLevel name="RosettaSrv" policyFile="rssrvpolicy.config" />
    </securityPolicy>
    <trust level="RosettaSrv" originUrl="" legacyCasModel="true" />
    <webServices>
      <soapExtensionTypes>
        <add type="Microsoft.ReportingServices.WebServer.RsSoapExtension, ReportingServicesWebServer" priority="1" group="1" />
      </soapExtensionTypes>
      <soapExtensionReflectorTypes>
        <add type="Microsoft.ReportingServices.WebServer.RsSoapExtensionReflector, ReportingServicesWebServer" />
      </soapExtensionReflectorTypes>
    </webServices>
  </system.web>
  <runtime>
    <alwaysFlowImpersonationPolicy enabled="true" />
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.Interfaces" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="8.0.242.0-14.0.0.0" newVersion="14.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingCore" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="9.0.242.0-14.0.0.0" newVersion="14.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingObjectModel" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="9.0.242.0-14.0.0.0" newVersion="14.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.SqlServer.Types" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="10.0.0.0-14.0.0.0" newVersion="14.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="msmgdsrv" publicKeyToken="89845dcd8080cc91" />
        <bindingRedirect oldVersion="9.0.0.0-14.0.0.0" newVersion="14.0.0.0" />
        <codeBase version="14.0.0.0" href="%ProgramFiles%\Microsoft Analysis Services\AS OLEDB\140\msmgdsrv.dll" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.Owin" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Cors" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-5.0.0.0" newVersion="5.2.3.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
  <system.net>
    <defaultProxy enabled="true" useDefaultCredentials="true">
      <proxy bypassonlocal="True" proxyaddress="http://ocs.kennisnet.nl:3128" />
    </defaultProxy>
  </system.net>
</configuration>

我发现了很多代码示例，但似乎都没有用，我设法创建了下面的代码，但是它不保存文件，而且我也不知道如何添加第二个键值。希望你们中的一个比我更熟练。

$file="web.config"
[xml]$xmlDoc = [System.Xml.XmlDocument](Get-Content $file)

$newEl=$xmlDoc.CreateElement("system.net")
$xmlDoc.configuration.AppendChild($newEl)  
$xmlDoc.Save($file)

$newEl=$xmlDoc.CreateElement("defaultProxy")   
$nameAtt1=$xmlDoc.CreateAttribute("enabled")
$nameAtt1.psbase.value="true"  
$newEl.SetAttributeNode($nameAtt1)  

$nameAtt2=$xmlDoc.CreateAttribute("useDefaultCredentials")  
$nameAtt2.psbase.value="true"    
$newEl.SetAttributeNode($nameAtt2) 
$xmlDoc.configuration["system.net"].AppendChild($newEl)  

$xmlDoc.Save($file)

最终结果需要创建完整的XML文件，如上所示。

请帮忙...