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public class Config
{
    public string TwitchClientId { get; }
    public string TwitchClientSecret { get; }
	
    public Config(string twitchClientId, string twitchClientSecret)
    {
        TwitchClientId = twitchClientId ?? throw new ArgumentNullException(nameof(twitchClientId));
        TwitchClientSecret = twitchClientSecret ?? throw new ArgumentNullException(nameof(twitchClientSecret));
    }
	
    public static Config FromFile(string path)
    {
        if (!File.Exists(path))
            throw new ArgumentException($"Config file cannot be found at path '{path}'.");
        var content = File.ReadAllText(path);
        return FromJson(content);
    }
	
    public static Config FromJson(string json)
    {
        var config = JsonConvert.DeserializeObject<Config>(json);
        if (config == null)
            throw new ArgumentException($"Argument 'json' has an invalid value: '{json}'.");
		
        return config;
    }
}

Config config = Config.FromFile("C:/path/to/file.json");