Why ConfigurationProvider Class's Data property is Protected?

[BrandoZhangTest]

I found the ConfigurationProvider Class's Data property is Protected, but it provide the method to get the key and value.

In my opinion, I couldn't understand why set it is protected.

If I want to list the asp.net core environment variable, we could only write a custom method to list all keys and then get value according to these keys.

Example:

        public static HashSet<string> GetFullKeyNames(this IConfigurationProvider provider, string rootKey, HashSet<string> initialKeys)
        {
            foreach (var key in provider.GetChildKeys(Enumerable.Empty<string>(), rootKey))
            {
                string surrogateKey = key;
                if (rootKey != null)
                {
                    surrogateKey = rootKey + ":" + key;
                }

                GetFullKeyNames(provider, surrogateKey, initialKeys);

                if (!initialKeys.Any(k => k.StartsWith(surrogateKey)))
                {
                    initialKeys.Add(surrogateKey);
                }
            }

            return initialKeys;
        }
    }


//Get the key value according to each provider

            var re =  ((ConfigurationRoot)Configuration).Providers.FirstOrDefault(x=>x.GetType() == typeof(EnvironmentVariablesConfigurationProvider));

            

            var directory = new Dictionary<string, string>();

            foreach (var key in re.GetFullKeyNames( null, new HashSet<string>()).OrderBy(p => p))
            {
                if (re.TryGet(key, out var value))
                {
                    directory.Add(key, value);
                 }
            }