Implementing JWT authentication in standalone Blazor WASM requires a custom AuthenticationStateProvider that reads the token and extracts claims to populate the user principal.

Flow Overview

1. User logs in — client POSTs credentials to API
2. API returns a JWT token
3. Client stores token in memory or localStorage
4. Custom AuthStateProvider parses token claims and populates ClaimsPrincipal
5. Components access user identity via AuthorizeView

Custom AuthenticationStateProvider

public class JwtAuthStateProvider : AuthenticationStateProvider
{
    public override async Task<AuthenticationState> GetAuthenticationStateAsync()
    {
        var token = await _storage.GetItemAsync<string>("auth_token");
        if (string.IsNullOrEmpty(token))
            return new AuthenticationState(new ClaimsPrincipal());

        var claims = ParseClaimsFromJwt(token);
        var identity = new ClaimsIdentity(claims, "jwt");
        return new AuthenticationState(new ClaimsPrincipal(identity));
    }
}

Register the Provider

builder.Services.AddScoped<AuthenticationStateProvider, JwtAuthStateProvider>();
builder.Services.AddAuthorizationCore();

Reference:

Wikipedia: JSON Web Token

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