How to run code on login in Blazor WebAssembly?

user_9475977 0
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I'm trying to run a function every time a user logs in. What I tried is to obtain an instance of AuthenticationStateProvider from the DI container and subscribe to its AuthenticationStateChanged event. The problem is that my login pages are implemented using server-rendered Razor Pages so the page refreshes after a successful login. This means that my code subscribes to the event after it is fired, so my handler function never runs. Can anybody see a way to run custom code upon successful login?

blazor-webassembly blazor events authentication c#
2 Answers

If you're using the token based authentication (API), you can attach an event handler to the RemoteAuthenticatorView component located in the Authentication component. I think it has an event that is invoked immediately after a user log in. As far as I recall, I've once answered a similar question that way, and then changed my answer to something more useful. Try this solution, and let us know if it's OK.

user_61528910

You can inject the AuthorizationService into your component and then await the AuthenticationState to run code if your user is logged in. Further details are in the documentation here.

@using Microsoft.AspNetCore.Authorization
@inject IAuthorizationService AuthorizationService

<button @onclick="@DoSomething">Do something important</button>

@code {
    [CascadingParameter]
    private Task<AuthenticationState> authenticationStateTask { get; set; }

    private async Task DoSomething()
    {
        var user = (await authenticationStateTask).User;

        if (user.Identity.IsAuthenticated)
        {
            // Perform an action only available to authenticated (signed-in) users.
        }
    }
}

Instead of an onclick handler you can put the auth check in a component's initializedasync method or wherever else is appropriate.

Another approach is to hook into the OnLoginSucceeded property of the RemoteAuthenticatorView, like:

<RemoteAuthenticatorView Action="@Action" OnLogInSucceeded="OnLoginSucceeded" />
@code{
    [Parameter] public string Action { get; set; }

    private void OnLoginSucceeded() 
    {
        // do your stuff here
    }
}
eking_189380
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