How to read values from custom section in web.config

I have added a custom section called secureAppSettings to my web.config file:

<configuration>
  <configSections>
    <section name="secureAppSettings" type="System.Configuration.NameValueSectionHandler, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
  </configSections>
  <secureAppSettings>
    <add key="userName" value="username"/>
    <add key="userPassword" value="password"/>
  </secureAppSettings>  
</configuration>

secureAppSettings is decrypted and has two keys inside it.

Now in my code, I tried to access the keys like this:

string userName = System.Configuration.ConfigurationManager.secureAppSettings["userName"];
string userPassword = System.Configuration.ConfigurationManager.secureAppSettings["userPassword"];

But null is returning for these fields.

How can I get the field values?