Share authentication cookies among ASP.NET apps

By Rick Anderson

Websites often consist of individual web apps working together. To provide a single sign-on (SSO) experience, web apps within a site must share authentication cookies. To support this scenario, the data protection stack allows sharing Katana cookie authentication and ASP.NET Core cookie authentication tickets.

In the examples that follow:

  • The authentication cookie name is set to a common value of .AspNet.SharedCookie.
  • The AuthenticationType is set to Identity.Application either explicitly or by default.
  • A common app name is used to enable the data protection system to share data protection keys (SharedCookieApp).
  • Identity.Application is used as the authentication scheme. Whatever scheme is used, it must be used consistently within and across the shared cookie apps either as the default scheme or by explicitly setting it. The scheme is used when encrypting and decrypting cookies, so a consistent scheme must be used across apps.
  • A common data protection key storage location is used.
  • DataProtectionProvider requires the Microsoft.AspNetCore.DataProtection.Extensions NuGet package:
  • SetApplicationName sets the common app name.

Share authentication cookies with ASP.NET Core Identity

When using ASP.NET Core Identity:

In Startup.ConfigureServices:

services.AddDataProtection()
    .PersistKeysToFileSystem("{PATH TO COMMON KEY RING FOLDER}")
    .SetApplicationName("SharedCookieApp");

services.ConfigureApplicationCookie(options => {
    options.Cookie.Name = ".AspNet.SharedCookie";
});

Note: The preceding instructions don't work with ITicketStore (CookieAuthenticationOptions.SessionStore). For more information, see this GitHub issue.

For security reasons, authentication cookies are not compressed in ASP.NET Core. When using authentication cookies, developers should minimize the number of claim information included to just that necessary for their needs.

Share authentication cookies without ASP.NET Core Identity

When using cookies directly without ASP.NET Core Identity, configure data protection and authentication in Startup.ConfigureServices. In the following example, the authentication type is set to Identity.Application:

services.AddDataProtection()
    .PersistKeysToFileSystem("{PATH TO COMMON KEY RING FOLDER}")
    .SetApplicationName("SharedCookieApp");

services.AddAuthentication("Identity.Application")
    .AddCookie("Identity.Application", options =>
    {
        options.Cookie.Name = ".AspNet.SharedCookie";
    });

For security reasons, authentication cookies are not compressed in ASP.NET Core. When using authentication cookies, developers should minimize the number of claim information included to just that necessary for their needs.

Share cookies across different base paths

An authentication cookie uses the HttpRequest.PathBase as its default Cookie.Path. If the app's cookie must be shared across different base paths, Path must be overridden:

services.AddDataProtection()
    .PersistKeysToFileSystem("{PATH TO COMMON KEY RING FOLDER}")
    .SetApplicationName("SharedCookieApp");

services.ConfigureApplicationCookie(options => {
    options.Cookie.Name = ".AspNet.SharedCookie";
    options.Cookie.Path = "/";
});

Share cookies across subdomains

When hosting apps that share cookies across subdomains, specify a common domain in the Cookie.Domain property. To share cookies across apps at contoso.com, such as first_subdomain.contoso.com and second_subdomain.contoso.com, specify the Cookie.Domain as .contoso.com:

options.Cookie.Domain = ".contoso.com";

Encrypt data protection keys at rest

For production deployments, configure the DataProtectionProvider to encrypt keys at rest with DPAPI or an X509Certificate. For more information, see Key encryption at rest in Windows and Azure using ASP.NET Core. In the following example, a certificate thumbprint is provided to ProtectKeysWithCertificate:

services.AddDataProtection()
    .ProtectKeysWithCertificate("{CERTIFICATE THUMBPRINT}");

Share authentication cookies between ASP.NET 4.x and ASP.NET Core apps

ASP.NET 4.x apps that use Katana Cookie Authentication Middleware can be configured to generate authentication cookies that are compatible with the ASP.NET Core Cookie Authentication Middleware. For more information, see Share authentication cookies between ASP.NET 4.x and ASP.NET Core apps (dotnet/AspNetCore.Docs #21987).

Use a common user database

When apps use the same Identity schema (same version of Identity), confirm that the Identity system for each app is pointed at the same user database. Otherwise, the identity system produces failures at runtime when it attempts to match the information in the authentication cookie against the information in its database.

When the Identity schema is different among apps, usually because apps are using different Identity versions, sharing a common database based on the latest version of Identity isn't possible without remapping and adding columns in other app's Identity schemas. It's often more efficient to upgrade the other apps to use the latest Identity version so that a common database can be shared by the apps.

Additional resources