如何在运行时修改web.config appSettings？

Configuration config = WebConfigurationManager.OpenWebConfiguration("~");
AppSettingsSection appSettings = (AppSettingsSection)config.GetSection("appSettings");
appSettings.Settings["key"].Value = "new_value";
config.Save();

$webConfigPath = "C:\inetpub\wwwroot\web.config"
$xml = [xml](Get-Content $webConfigPath)
$xml.configuration.appSettings.add | ? { $_.key -eq "key" } | % { $_.value = "new_value" }
$xml.Save($webConfigPath)

var fs = require('fs');
var xml2js = require('xml2js');
var parser = new xml2js.Parser();
var builder = new xml2js.Builder();

fs.readFile('web.config', function(err, data) {
  parser.parseString(data, function(err, result) {
    result.configuration.appSettings.add.forEach(function(add) {
      if (add.$.key === 'key') {
        add.$.value = 'new_value';
      }
    });
    var xml = builder.buildObject(result);
    fs.writeFile('web.config', xml, function(err) {
      if (err) throw err;
      console.log('web.config updated');
    });
  });
});