Blazor WASM runs in the browser but C# cannot access browser storage APIs directly. You need JS interop or a library wrapper to read and write localStorage and sessionStorage.

Using Blazored.LocalStorage Library

// Install: dotnet add package Blazored.LocalStorage

// Program.cs:
builder.Services.AddBlazoredLocalStorage();

// Component:
@inject ILocalStorageService LocalStorage

private async Task SaveToken(string token)
    => await LocalStorage.SetItemAsync("auth_token", token);

private async Task<string> GetToken()
    => await LocalStorage.GetItemAsync<string>("auth_token");

Manual JS Interop Approach

await JS.InvokeVoidAsync("localStorage.setItem", "key", "value");
string val = await JS.InvokeAsync<string>("localStorage.getItem", "key");

Storage Rules

• localStorage persists across sessions; sessionStorage clears on tab close
• Both are limited to ~5MB per origin
• Never store sensitive data — localStorage is accessible via JavaScript and vulnerable to XSS
• Use short-lived JWT tokens stored in memory when security is critical

Reference:

Wikipedia: Web Storage

https://en.wikipedia.org/wiki/Web_storage