In .NET Core 2.0, reducing the size of identity cookies involves optimizing the cookie payload to store only essential data and removing unnecessary data to reduce the overall cookie size. Smaller cookies can improve performance, especially for requests made with cookies in the headers.

Here are some strategies to reduce the size of identity cookies in .NET Core 2.0:

  1. Limit Claims Stored in the Cookie: By default, the identity cookie in .NET Core includes all user claims. If you have many claims, consider only storing essential claims in the cookie. Claims that are not required for every request can be stored in the user's session or fetched from the database when needed.

    In your Startup.cs, configure the CookieAuthenticationOptions to specify the claims to include in the cookie:

csharp
services.ConfigureApplicationCookie(options => { // Only include essential claims in the cookie options.ClaimsIssuer = "myissuer"; options.Events = new CookieAuthenticationEvents { // Implement the OnSigningIn event to customize the claims stored in the cookie OnSigningIn = async context => { var claimsIdentity = (ClaimsIdentity)context.Principal.Identity; // Remove unnecessary claims from the identity claimsIdentity.RemoveClaim(claimsIdentity.FindFirst("unneeded_claim")); } }; });
  1. Use Custom Serialization: By default, .NET Core uses JSON serialization to store the claims in the cookie. You can use a custom serializer to optimize the payload size. For example, if your claims contain simple data, you can use a custom serializer like MessagePack to reduce the cookie size further.

  2. Enable Data Protection Compression (ASP.NET Core 2.1+): If you are using ASP.NET Core 2.1 or later, you can enable data protection compression to compress the cookie data. This can significantly reduce the cookie size for large payloads.

    In your Startup.cs, add the following code to enable data protection compression:

csharp
public void ConfigureServices(IServiceCollection services) { // ... services.AddDataProtection() .UseCryptographicAlgorithms(new AuthenticatedEncryptorConfiguration() { EncryptionAlgorithm = EncryptionAlgorithm.AES_256_CBC, ValidationAlgorithm = ValidationAlgorithm.HMACSHA256 }) .UseCompression(); // ... }
  1. Limit Authentication Cookie Size: You can limit the maximum size of the authentication cookie by setting the CookieAuthenticationOptions property Cookie.SecurePolicy to CookieSecurePolicy.Always and CookieManager property Options to limit the maximum size.
csharp
services.Configure<CookieAuthenticationOptions>(IdentityConstants.ApplicationScheme, options => { options.Cookie.SecurePolicy = CookieSecurePolicy.Always; options.CookieManager.Options.MaximumSize = 4096; // Set the maximum cookie size in bytes });

Remember that reducing the size of identity cookies should be done with caution. Ensure that essential data is included in the cookie to maintain proper authentication and authorization. Removing critical claims from the cookie may lead to security vulnerabilities or inconsistent behavior in the application. Always perform adequate testing after making changes to ensure your application functions as expected.

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