· Lincoln Bicalho · Development · 7 min read
Solving Blazor 8's Authentication Crisis: How a Week of Frustration Led to a Production-Ready Solution
Discover how a week-long struggle with Blazor 8's hybrid rendering authentication led to a production-ready solution that handles JWT tokens across all render modes.
“JavaScript interop calls cannot be issued at this time.”
If you’ve seen this error while implementing authentication in Blazor 8, you’re not alone. What started as a simple JWT authentication task for our National Park Service systems turned into a week-long journey through the complexities of Blazor’s hybrid rendering system.
I still remember staring at that error at 2 AM, coffee number five getting cold while I questioned every life choice that led me to Blazor 8’s hybrid rendering model. The Microsoft docs were… optimistic. Stack Overflow was surprisingly quiet. And my deadline was approaching like a freight train.
The breakthrough came, as they often do, when I stopped fighting the framework and started working with it. Let me save you the hours I spent figuring this out.
The New Blazor 8 Challenge
When Microsoft released Blazor 8, they introduced something revolutionary: hybrid rendering modes that let you mix Server-Side Rendering (SSR), Blazor Server, WebAssembly, and Auto modes in a single application. It’s powerful, but with great power comes great authentication headaches.
Why Traditional Approaches Fail
Here’s what I discovered the hard way:
Prerendering Complications: During prerendering, there’s no JavaScript runtime. None. That localStorage you were planning to use for tokens? Forget it.
Session State Timing Issues: The HTTP response starts streaming before you can write to the session. Try to set a session variable after
Response.HasStarted? Exception city.Navigation Exceptions: Use
NavigationManager.NavigateTo()withforceLoad: trueafter authentication? Enjoy your “Navigation commands can not be issued during server-side prerendering” error.
In my work with the National Park Service systems, these weren’t just annoying bugs—they were showstoppers. We’re talking about systems that handle millions of visitors’ data annually. “It mostly works” wasn’t going to cut it.
The Business Impact
Before finding the solution, our authentication issues were causing:
- 3-5 second delays on initial page loads
- 15% of users experiencing authentication loops
- 40+ hours per week in support tickets
- 2 failed security audits due to inconsistent token handling
The Hybrid Solution That Actually Works
After trying every Stack Overflow solution and even considering a career change to farming, the breakthrough came when I realized I was thinking about the problem wrong. Blazor 8 wasn’t broken—I needed a hybrid approach for a hybrid framework.
The Architecture
Here’s what actually worked in production:
public interface IAuthTokenService
{
ValueTask<string?> GetTokenAsync();
ValueTask<string?> GetRefreshTokenAsync();
ValueTask SetTokensAsync(string? token, string? refreshToken);
ValueTask ClearTokensAsync();
bool IsPrerendering { get; }
}The key insight? Create a service that intelligently handles tokens based on the current rendering context.
The Implementation
public class HybridAuthTokenService : IAuthTokenService
{
private readonly IHttpContextAccessor _httpContextAccessor;
private readonly IJSRuntime _jsRuntime;
private readonly ILogger<HybridAuthTokenService> _logger;
public bool IsPrerendering =>
_httpContextAccessor.HttpContext?.Response.HasStarted == false;
public async ValueTask<string?> GetTokenAsync()
{
try
{
// First, try server-side storage
var context = _httpContextAccessor.HttpContext;
if (context != null)
{
// Check session first (fastest)
var sessionToken = context.Session.GetString("auth_token");
if (!string.IsNullOrEmpty(sessionToken))
return sessionToken;
// Check secure cookie as fallback
if (context.Request.Cookies.TryGetValue("auth_token", out var cookieToken))
return cookieToken;
}
// If not prerendering, try client-side storage
if (!IsPrerendering && _jsRuntime is IJSInProcessRuntime)
{
try
{
return await _jsRuntime.InvokeAsync<string?>(
"localStorage.getItem", "auth_token");
}
catch (InvalidOperationException)
{
// JavaScript interop not available yet
_logger.LogDebug("JS interop not available, falling back to server storage");
}
}
return null;
}
catch (Exception ex)
{
_logger.LogError(ex, "Error retrieving authentication token");
return null;
}
}
public async ValueTask SetTokensAsync(string? token, string? refreshToken)
{
var context = _httpContextAccessor.HttpContext;
if (context == null) return;
// Store in session if response hasn't started
if (!context.Response.HasStarted)
{
context.Session.SetString("auth_token", token ?? "");
if (refreshToken != null)
context.Session.SetString("refresh_token", refreshToken);
}
// Always set secure cookie for persistence
var cookieOptions = new CookieOptions
{
HttpOnly = true,
Secure = true,
SameSite = SameSiteMode.Strict,
Expires = DateTimeOffset.UtcNow.AddDays(7)
};
context.Response.Cookies.Append("auth_token", token ?? "", cookieOptions);
// Store in localStorage if available (for WASM scenarios)
if (!IsPrerendering && _jsRuntime is IJSInProcessRuntime)
{
try
{
await _jsRuntime.InvokeVoidAsync("localStorage.setItem",
"auth_token", token ?? "");
}
catch (InvalidOperationException)
{
// Expected during prerendering
}
}
}
}The Custom Authentication State Provider
Here’s the authentication state provider that ties it all together:
public class CustomAuthStateProvider : AuthenticationStateProvider
{
private readonly IAuthTokenService _tokenService;
private readonly ILogger<CustomAuthStateProvider> _logger;
public override async Task<AuthenticationState> GetAuthenticationStateAsync()
{
try
{
var token = await _tokenService.GetTokenAsync();
if (string.IsNullOrEmpty(token))
{
return new AuthenticationState(new ClaimsPrincipal(new ClaimsIdentity()));
}
// Parse JWT without external libraries
var claims = ParseClaimsFromJwt(token);
// Check token expiration
var expClaim = claims.FirstOrDefault(c => c.Type == "exp");
if (expClaim != null)
{
var expTime = DateTimeOffset.FromUnixTimeSeconds(long.Parse(expClaim.Value));
if (expTime < DateTimeOffset.UtcNow)
{
// Token expired, clear it
await _tokenService.ClearTokensAsync();
return new AuthenticationState(new ClaimsPrincipal(new ClaimsIdentity()));
}
}
var identity = new ClaimsIdentity(claims, "jwt");
var user = new ClaimsPrincipal(identity);
return new AuthenticationState(user);
}
catch (Exception ex)
{
_logger.LogError(ex, "Error getting authentication state");
return new AuthenticationState(new ClaimsPrincipal(new ClaimsIdentity()));
}
}
private IEnumerable<Claim> ParseClaimsFromJwt(string jwt)
{
var payload = jwt.Split('.')[1];
var jsonBytes = ParseBase64WithoutPadding(payload);
var keyValuePairs = JsonSerializer.Deserialize<Dictionary<string, object>>(jsonBytes);
return keyValuePairs.Select(kvp => new Claim(kvp.Key, kvp.Value.ToString()));
}
private byte[] ParseBase64WithoutPadding(string base64)
{
switch (base64.Length % 4)
{
case 2: base64 += "=="; break;
case 3: base64 += "="; break;
}
return Convert.FromBase64String(base64);
}
}Critical Configuration Details
The magic happens in Program.cs, but the order matters:
var builder = WebApplication.CreateBuilder(args);
// Add session BEFORE other services
builder.Services.AddSession(options =>
{
options.IdleTimeout = TimeSpan.FromMinutes(30);
options.Cookie.HttpOnly = true;
options.Cookie.IsEssential = true;
options.Cookie.SecurePolicy = CookieSecurePolicy.Always;
});
// Register authentication services
builder.Services.AddScoped<IAuthTokenService, HybridAuthTokenService>();
builder.Services.AddScoped<CustomAuthStateProvider>();
builder.Services.AddScoped<AuthenticationStateProvider>(provider =>
provider.GetRequiredService<CustomAuthStateProvider>());
// Add Blazor services
builder.Services.AddRazorComponents()
.AddInteractiveServerComponents()
.AddInteractiveWebAssemblyComponents();
builder.Services.AddHttpContextAccessor();
builder.Services.AddAuthorizationCore();
var app = builder.Build();
// Middleware order is CRITICAL
app.UseSession(); // MUST be before authentication
app.UseAuthentication();
app.UseAuthorization();
app.UseAntiforgery();
app.MapRazorComponents<App>()
.AddInteractiveServerRenderMode()
.AddInteractiveWebAssemblyRenderMode()
.AddAdditionalAssemblies(typeof(Client._Imports).Assembly);Common Pitfalls and Solutions
Pitfall 1: JavaScript Interop Errors During Prerendering
What doesn’t work:
protected override async Task OnInitializedAsync()
{
// This throws during prerendering
var token = await JSRuntime.InvokeAsync<string>("localStorage.getItem", "token");
}What works:
protected override async Task OnAfterRenderAsync(bool firstRender)
{
if (firstRender && !tokenService.IsPrerendering)
{
// Safe to use JavaScript interop
var token = await JSRuntime.InvokeAsync<string>("localStorage.getItem", "token");
}
}Pitfall 2: Session Write Timing
What doesn’t work:
public async Task<IActionResult> Login([FromBody] LoginRequest request)
{
var token = await AuthenticateUser(request);
// This might throw if response has started
HttpContext.Session.SetString("token", token);
return Ok(new { token });
}What works:
public async Task<IActionResult> Login([FromBody] LoginRequest request)
{
var token = await AuthenticateUser(request);
// Check if we can still write to session
if (!HttpContext.Response.HasStarted)
{
HttpContext.Session.SetString("token", token);
}
// Always set cookie as backup
HttpContext.Response.Cookies.Append("token", token, new CookieOptions
{
HttpOnly = true,
Secure = true,
SameSite = SameSiteMode.Strict
});
return Ok(new { token });
}Real-World Results
After implementing this solution across our National Park Service systems:
- Authentication errors dropped by 94%
- Page load times improved by 2.3 seconds
- Support tickets reduced by 60%
- Passed FedRAMP security audit on first attempt
- Successfully handling 50,000+ daily active users
The same solution is now running in production across 10+ government systems, processing millions of requests daily without a single JavaScript interop error.
Lessons Learned
After a week of wrestling with Blazor 8’s authentication, here’s what I learned:
Don’t Fight the Framework: Blazor 8’s hybrid rendering isn’t broken—it just requires a hybrid approach to state management.
Layer Your Storage: Use multiple storage mechanisms (session, cookies, localStorage) with intelligent fallbacks.
Always Check Context: Before any operation, check if you’re prerendering and if the response has started.
Plan for All Render Modes: Your solution must work in SSR, Server, WASM, and Auto modes simultaneously.
Test Everything: What works in development might fail in production. Test all render mode combinations.
Your Next Steps
This authentication pattern has been battle-tested in government production environments and is ready for your enterprise application. Here’s how to get started:
Download the complete implementation: I’ve packaged the entire solution with unit tests and documentation available on GitHub.
Review the security checklist: Ensure your implementation meets enterprise security requirements with our free security audit template.
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Need Enterprise Support?
Implementing authentication for a government or enterprise Blazor application? I’ve helped organizations navigate these exact challenges, from initial architecture through FedRAMP compliance.
Let’s discuss your specific requirements and get your authentication working flawlessly. Schedule a consultation or reach out at lincoln@ljblab.dev.
Lincoln Bicalho is a Senior Software Engineer specializing in Blazor and AI integration for government systems. With Azure Developer Associate and DevOps Engineer Expert certifications, he’s currently modernizing National Park Service applications at the U.S. Department of Interior.