C# XML config file custom section always null

Working on a VSTO Outlook addin. I need to store configuration parameters in an XML file. I am struggling with some basic config file loading issue. I would appreciate a fresh view:

customConfiguration.xml

<?xml version="1.0" encoding="utf-8"?>
<configuration>

  <configSections>
      <section name="CDSSettings"  type="System.Configuration.NameValueSectionHandler" />
  </configSections>

  <CDSSettings>
    <add key="APIusername" value="myUser" />
    <add key="APIpassword" value="myPassword" />
  </CDSSettings>

    <appSettings>
      <add key="logLevel" value="0" /> 
  </appSettings>
</configuration>

Code

ExeConfigurationFileMap map = new ExeConfigurationFileMap();
map.ExeConfigFilename = "customConfiguration.xml";
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);

AppSettingsSection appSettingsSection = (config.GetSection("appSettings") as AppSettingsSection);
// --> All ok

ConfigurationSection CDSSettings = (ConfigurationSection)config.GetSection("CDSSettings");
// --> How to get the APIusername key?

Any chance I can avoid an XML parser or SectionInformation.GetRawXml()?