Custom Token Authentication in Blazor Server with ASP.NET Core API

Custom Token Authentication in Blazor Server with ASP.NET Core API

In modern web development, securing APIs is crucial. This blog explains how to implement a simple yet secure token-based authentication system in a Blazor Server application using ASP.NET Core Web API.

This is especially useful when you don’t want to rely on JWT or external identity providers and need a custom implementation tailored to your app.

🔐 Key Concepts Covered

  • Logging in and returning a GUID-based access token
  • Storing the token in localStorage (with JS interop)
  • Sending the token via headers on future API requests
  • Validating the token on the server using a custom authentication handler
  • Protecting your API using the [Authorize] attribute
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📦 Custom AuthenticationHandler

public class TokenAuthenticationHandler : AuthenticationHandler<AuthenticationSchemeOptions> { protected override Task<AuthenticateResult> HandleAuthenticateAsync() { if (!Request.Headers.TryGetValue("X-Access-Token", out var tokenValue)) return Task.FromResult(AuthenticateResult.Fail("Token missing")); var token = tokenValue.FirstOrDefault(); // Validate token from DB and create claims ... } }

🔧 Program.cs Setup

builder.Services.AddAuthentication("TokenScheme") .AddScheme<AuthenticationSchemeOptions, TokenAuthenticationHandler>("TokenScheme", null); app.UseAuthentication(); app.UseAuthorization();

✅ Secure API with [Authorize]

[ApiController] [Route("api/[controller]")] [Authorize] public class UserController : ControllerBase { [HttpGet("me")] public IActionResult Me() => Ok(User.Identity.Name); }

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