Json.Masker.SystemTextJson 1.1.14

Json.Masker

Json.Masker is a lightweight library for masking sensitive values during JSON serialization.
Mark properties with [Sensitive], enable the masking context, and the rest happens automatically—no custom DTOs or fragile string hacks.

Supports both Newtonsoft.Json and System.Text.Json.

Packages

Quick Start

Install the package for your serializer:

dotnet add package Json.Masker.Newtonsoft
# or
dotnet add package Json.Masker.SystemTextJson

# optional ASP.NET helpers
dotnet add package Json.Masker.AspNet
dotnet add package Json.Masker.AspNet.Newtonsoft

The ASP.NET helpers let you toggle masking per request with zero boilerplate.

Setup

Option 1: Dependency Injection

builder.Services.AddJsonMasking(options =>
{
    // Replace with a custom IMaskingService if needed
    options.MaskingService = new DefaultMaskingService();
});

builder.Services
    .AddOptions<MvcNewtonsoftJsonOptions>()
    .Configure<IJsonMaskingConfigurator>((opts, configurator) =>
        configurator.Configure(opts.SerializerSettings));

app.UseNewtonsoftJsonMasking();

Swap Newtonsoft for System.Text.Json as needed:

builder.Services.AddControllers();
builder.Services.AddJsonMasking();

builder.Services
    .AddOptions<JsonOptions>()
    .Configure<IJsonMaskingConfigurator>((opts, configurator) =>
        configurator.Configure(opts.SerializerOptions));

app.UseTextJsonMasking();

DI automatically registers:

• IMaskingService (default or custom)
• IJsonMaskingConfigurator (serializer-specific configurator)

Option 2: Manual Setup

Newtonsoft.Json

var masking = new DefaultMaskingService();
var settings = new JsonSerializerSettings
{
    ContractResolver = new MaskingContractResolver(masking)
};

var json = JsonConvert.SerializeObject(customer, Formatting.Indented, settings);

System.Text.Json

var masking = new DefaultMaskingService();
var options = new JsonSerializerOptions
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver
    {
        Modifiers = { new MaskingTypeInfoModifier(masking).Modify }
    }
};

var json = JsonSerializer.Serialize(customer, options);

Masking Example

public class Customer
{
    public string Name { get; set; } = string.Empty;

    [Sensitive(MaskingStrategy.Creditcard)]
    public string CreditCard { get; set; } = string.Empty;

    [Sensitive(MaskingStrategy.Ssn)]
    public string SSN { get; set; } = string.Empty;

    [Sensitive(MaskingStrategy.Email)]
    public string Email { get; set; } = string.Empty;

    [Sensitive(MaskingStrategy.Iban)]
    public string BankAccount { get; set; } = string.Empty;

    [Sensitive] public int Age { get; set; }

    [Sensitive(MaskingStrategy.Redacted)]
    public List<string> Hobbies { get; set; } = [];

    [Sensitive("##-****-####")]
    public string LoyaltyNumber { get; set; } = string.Empty;
}

Enable masking for the current scope:

MaskingContextAccessor.Set(new MaskingContext { Enabled = true });

Result:

{
  "Name": "Alice",
  "CreditCard": "****-****-****-1234",
  "SSN": "***-**-6789",
  "Email": "a*****@g****.com",
  "BankAccount": "GB** **** **** **** 1234",
  "Age": "****",
  "Hobbies": ["<redacted>", "<redacted>"],
  "LoyaltyNumber": "12-****-3456"
}

Masking Strategies

Custom masking logic? Implement IMaskingService and register it via MaskingOptions.

Contributing

1. dotnet restore, dotnet build, dotnet test
2. Run ./install-dependencies.sh to sync the expected .NET SDK and git hooks.
3. Run ./run-pre-commit.sh to check analyzers and formatters.
4. Open a PR with conventional commits; merging to main triggers NuGet release.

Extending Masking

To add a new masking rule:

1. Implement IMaskingService or subclass DefaultMaskingService.
2. Add tests under tests/Json.Masker.Tests.
3. (Optional) Contribute back via a new MaskingStrategy value.

Adding Serializer Support

To integrate another serializer:

1. Create a project under src/ referencing Json.Masker.Abstract.
2. Implement IJsonMaskingConfigurator.
3. Expose an AddJsonMasking extension.
4. Add integration tests to ensure sensitive data is masked.

Performance

Build & Test

dotnet restore
dotnet build
dotnet test

Run ./install-dependencies.sh to install matching SDKs and pre-commit hooks.

Samples

Check out /samples for minimal demos:

• System.Text.Json: Json.Masker.Sample.SystemTextJson
• Newtonsoft.Json: Json.Masker.Sample.Newtonsoft

Run with:

dotnet run --project <sample-project>

View masked and unmasked outputs side-by-side in your favorite REST client. Note: in order to see masked output make sure to include 'X-Json-Mask: true' in the request headers.