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title IHttpContextAccessor/HttpContext in ASP.NET Core Blazor apps
author guardrex
description Learn about IHttpContextAccessor and HttpContext in ASP.NET Core Blazor apps.
monikerRange >= aspnetcore-3.1
ms.author wpickett
ms.custom mvc
ms.date 11/11/2025
uid blazor/components/httpcontext

IHttpContextAccessor/HttpContext in ASP.NET Core Blazor apps

[!INCLUDE]

:::moniker range=">= aspnetcore-8.0"

xref:Microsoft.AspNetCore.Http.IHttpContextAccessor generally should be avoided with interactive rendering because a valid xref:Microsoft.AspNetCore.Http.HttpContext isn't always available.

xref:Microsoft.AspNetCore.Http.IHttpContextAccessor can be used during static server-side rendering (static SSR), for example in statically-rendered root components, and when using a token handler for web API calls on the server. We recommend avoiding xref:Microsoft.AspNetCore.Http.IHttpContextAccessor when static SSR or code running on the server can't be guaranteed.

xref:Microsoft.AspNetCore.Http.HttpContext can be used as a cascading parameter only in statically-rendered root components or during static SSR for general tasks, such as inspecting and modifying headers or other properties in the App component (App.razor). The value is null during interactive rendering.

[CascadingParameter]
private HttpContext? HttpContext { get; set; }

For additional context in advanced edge cases†, see the discussion in the following articles:

†Most developers building and maintaining Blazor apps don't need to delve into advanced concepts when the general guidance in this article is followed. The most important concept to keep in mind is that xref:Microsoft.AspNetCore.Http.HttpContext is fundamentally a server-based, request-response feature that's only generally available on the server during static SSR and only created when a user's circuit is established.

Don't set or modify headers after the response starts

Attempting to set or modify a header after the first rendering (after the response starts) results in an error:

:::no-loc text="System.InvalidOperationException: 'Headers are read-only, response has already started.'":::

Examples of situations that result in this error include:

  • Calling xref:Microsoft.AspNetCore.Identity.SignInManager%601.PasswordSignInAsync%2A?displayProperty=nameWithType, which must set headers for Identity to function correctly, while adopting streaming rendering.
  • Attempting to set or modify a header after the response has started during interactive rendering.

For guidance on setting headers before the response starts, see xref:blazor/fundamentals/startup#control-headers-in-c-code.

:::moniker-end

:::moniker range="< aspnetcore-8.0"

Don't use xref:Microsoft.AspNetCore.Http.IHttpContextAccessor/xref:Microsoft.AspNetCore.Http.HttpContext directly or indirectly in the Razor components of server-side Blazor apps. Blazor apps run outside of the ASP.NET Core pipeline context. The xref:Microsoft.AspNetCore.Http.HttpContext isn't guaranteed to be available within the xref:Microsoft.AspNetCore.Http.IHttpContextAccessor, and xref:Microsoft.AspNetCore.Http.HttpContext isn't guaranteed to hold the context that started the Blazor app.

The recommended approach for passing request state to the Blazor app is through root component parameters during the app's initial rendering. Alternatively, the app can copy the data into a scoped service in the root component's initialization lifecycle event for use across the app. For more information, see xref:blazor/security/additional-scenarios#pass-tokens-to-a-server-side-blazor-app.

A critical aspect of server-side Blazor security is that the user attached to a given circuit might become updated at some point after the Blazor circuit is established but the xref:Microsoft.AspNetCore.Http.IHttpContextAccessor isn't updated. For more information on addressing this situation with custom services, see xref:blazor/security/additional-scenarios#circuit-handler-to-capture-users-for-custom-services.

:::moniker-end

For guidance on xref:Microsoft.AspNetCore.Http.IHttpContextAccessor and xref:Microsoft.AspNetCore.Http.HttpContext in ASP.NET Core SignalR, see xref:signalr/httpcontext.