Nefarius.Legacy.DataProtector 1.1.3

Nefarius.Legacy.DataProtector

ASP.NET Data Protection key store using EF (Legacy and Core).

Motivation

Recently I was tasked with the challenge of starting migrating an ASP.NET 4 MVC monolith over to the sacred .NET core universe. Since no direct upgrade paths exist, a common strategy is to gradually migrate over app logic to a new backend-frontend-combination while keeping the old app on life support and incorporated with the new software stack. A major pain-point is modernizing authentication and giving users an acceptable SSO experience. One such strategy is shared auth cookies between the ASP.NET Classic and Core apps.

Session cookies are encrypted by default, so both app environments need to have means to decrypt the session details. ASP.NET Core Data Protection is used to offload encryption and decryption, and the key material can be shared by a common filesystem directory or other means.

Since I already had to deal with EF (Core) and an MS SQL Server, I chose to backport an EF-based SQL Server backed key repository consumable both in ASP.NET Classic and Core from a single class library.

Usage

The main advantage is getting SSO via shared cookies to work while not relying on a shared directory, but SQL database instead. The example below assumes you have an ASP.NET Core backend playing reverse proxy to a legacy ASP.NET 4.x app and share the user session via cookie that gets decrypted via the DB-backed keys.

ASP.NET Core (.NET 8)

builder.Services.AddDbContext<DataProtectionDbContext>(options =>
    options.UseSqlServer(builder.Configuration.GetConnectionString("DataProtection")));

builder.Services.AddDataProtection()
    .PersistKeysToSqlServer(builder.Configuration.GetConnectionString("DataProtection")!)    
    .SetApplicationName("iis-app-name");

// example to use SSO via shared cookie with ASP.NET 4 
builder.Services.AddAuthentication(options =>
    {
        options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
    })
    // Shared cookie authentication
    .AddCookie(options =>
    {
        options.Cookie.Name = ".AspNet.SharedCookie";
        options.Cookie.SameSite = SameSiteMode.Lax;
        options.Cookie.Path = "/";
        options.Cookie.HttpOnly = true;
        options.Cookie.IsEssential = true;
        options.ExpireTimeSpan = TimeSpan.FromMinutes(120);
    })

ASP.NET 4 (.NET Framework)

// assumes OwinStartup is used

string connectionString = ConfigurationManager.ConnectionStrings["DataProtection"].ConnectionString;

app.UseCookieAuthentication(new CookieAuthenticationOptions
{
    AuthenticationType = CookieAuthenticationDefaults.AuthenticationType,
    CookieName = ".AspNet.SharedCookie",
    CookieSameSite = SameSiteMode.Lax,
    SlidingExpiration = true,
    ExpireTimeSpan = TimeSpan.FromMinutes(120),
    TicketDataFormat = new AspNetTicketDataFormat(
        new DataProtectorShim(
            SqlDataProtectionProvider.Create(connectionString, "iis-app-name")
                .CreateProtector(
                    "Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationMiddleware",
                    "Cookies",
                    "v2"))),
    CookieManager = new ChunkingCookieManager()
});

Documentation

Link to API docs.

Sources & 3rd party credits

• Key storage providers in ASP.NET Core / Entity Framework Core