single sign-on (SSO) between ASP.NET Core app and ASP.NET Web Forms app

Yes, you can achieve single sign-on (SSO) between your ASP.NET Core app and your legacy ASP.NET Web Forms app using a shared authentication token, typically a JWT (JSON Web Token). Here's a high-level approach to make this work:

🛠️ Strategy Overview

1. Authenticate in ASP.NET Core

   • Use ASP.NET Core Identity or any other authentication mechanism.

   • Generate a JWT token upon successful login.

2. Pass the Token to Web Forms App

   • Redirect the user to the Web Forms app with the token in the query string or a cookie.

   • Example: https://webformsapp.com?token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...

3. Validate Token in Web Forms

   • In the Web Forms app, intercept the token (e.g., in Global.asax or a base page).

   • Use a JWT library (like System.IdentityModel.Tokens.Jwt) to validate the token.

   • If valid, create a session or authentication cookie for the Web Forms app.

4. Secure the Token Exchange

   • Use HTTPS to prevent token leakage.

   • Sign the JWT with a shared secret or certificate.

   • Set a short expiration time and consider IP or user-agent binding.

🔐 Token Validation in Web Forms (Example)

var token = Request.QueryString["token"];
var tokenHandler = new JwtSecurityTokenHandler();
var validationParameters = new TokenValidationParameters
{
    ValidateIssuer = true,
    ValidIssuer = "your-core-app",
    ValidateAudience = true,
    ValidAudience = "your-webforms-app",
    ValidateLifetime = true,
    IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8.GetBytes("your-secret-key"))
};

SecurityToken validatedToken;
var principal = tokenHandler.ValidateToken(token, validationParameters, out validatedToken);

// Create session or cookie
Session["User"] = principal.Identity.Name;

✅ Best Practices

• Use same domain or subdomains if possible to share cookies.

• Consider using OpenID Connect or OAuth2 if both apps can support it.

• Store minimal user info in the token (e.g., user ID, roles).

• Rotate signing keys periodically.