Configuration をログに

BuildConfigurationLog.cs

string BuildConfigurationLog(IConfiguration configuration)
{
    var stringBuilder = new StringBuilder();
    foreach (var child in configuration.GetChildren())
    {
        if (child.Value == null)
        {
            TraverseConfiguration(child, stringBuilder);
        }
        else
        {
            // Value != null は文字列が設定されているもの
            // ルートで文字列なのはだいたい環境変数なのでスキップする
        }
    }
    return stringBuilder.ToString();

    void TraverseConfiguration(IConfigurationSection section, StringBuilder sb)
    {
        if (section.Value is null)
        {
            var children = section.GetChildren();
            if (children != null)
            {
                foreach (var child in children)
                {
                    TraverseConfiguration(child, sb);
                }
                return;
            }
        }
        sb.AppendLine($"{section.Path}: {MaskSecrets(section)}");
    }

    string MaskSecrets(IConfigurationSection section)
    {
        if (section.Key.EndsWith("Key", StringComparison.OrdinalIgnoreCase) ||
            section.Key.Contains("Password", StringComparison.OrdinalIgnoreCase) ||
            section.Key.Contains("Secret", StringComparison.OrdinalIgnoreCase) ||
            section.Key.Contains("Token", StringComparison.OrdinalIgnoreCase))
        {
            return $"<Secret Hash={HashString(section.Value)}>";
        }
        else
        {
            return Regex.Replace(section.Value, "(password|authtoken)=([^;]+)", (m) => $"{m.Groups[1].Value}=<Secret Hash={HashString(m.Groups[2].Value)}>", RegexOptions.IgnoreCase);
        }
    }

    string HashString(string value)
    {
        using (var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(typeof(Program).Assembly.FullName)))
        {
            return String.Concat(hmac.ComputeHash(Encoding.UTF8.GetBytes(value)).Select(x => x.ToString("x2"))).Substring(0, 6);
        }
    }
}