How to get message session/endpoint with generic host?

Question

I'm running a few NServiceBus endpoints that are built using the generic host configuration (https://docs.particular.net/samples/hosting/generic-host/). These endpoints run in Docker containers. Now, I want to schedule a message (with hangfire). Whenever the scheduled message is executed, I get the following error:

Value cannot be null. (Parameter 'session')

System.ArgumentNullException: Value cannot be null. (Parameter 'session')
   at NServiceBus.Guard.AgainstNull(String argumentName, Object value)
   at NServiceBus.IMessageSessionExtensions.Send(IMessageSession session, Object message)
   at Provisioning.Handlers.CustomerCreatedHandler.Reauthenticate(Guid customerId) in /src/Provisioning/Handlers/CustomerCreatedHandler.cs:line 30

This is because the Send() method doesn't have a message session. However, how do I obtain this session? Looking at https://docs.particular.net/nservicebus/hosting/, you can create a session by starting a new endpoint from a EndpointConfiguration. Since I use generic host, I only have the EndpointConfiguration but I don't have access to the endpoint that is created from this (or at least I don't know how to). This is what my configuration looks like (extremely simplified):

hostBuilder = Host.CreateDefaultBuilder()
    .UseConsoleLifetime()
    .UseNServiceBus(xtc =>
    {
        var endpointConfiguration = new EndpointConfiguration("endpointName");
        endpointConfiguration.UseSerialization<NewtonsoftSerializer>();
        endpointConfiguration.EnableInstallers();
        endpointConfiguration.DefineCriticalErrorAction(OnCriticalError);

        // removed all config

        return endpointConfiguration;
    });

And this is started with:

await hostBuilder.Build().RunAsync();

I'm using NServiceBus 7 by the way.

Edit:

This is how I schedule the Hangfire task (updated based on Szymon's answer, but not working yet):

public class CustomerCreatedHandler : IHandleMessages<CustomerCreated>
{
    private static IServiceProvider _provider;

    public CustomerCreatedHandler(IServiceProvider provider)
    {
        _provider = provider;
    }

    public async Task Handle(CustomerCreated message, IMessageHandlerContext context)
    {
        RecurringJob.AddOrUpdate($"Reauthenticate-{message.CustomerId}", () => Reauthenticate(message.CustomerId), Cron.Hourly);
    }

    public static Task Reauthenticate(Guid customerId)
    {
        IMessageSession session = _provider.GetService<IMessageSession>();
        return session.Send(new AuthenticateCustomer { CustomerId = customerId });
    }
}

It results in:

System.ArgumentNullException
Value cannot be null. (Parameter 'provider')

System.ArgumentNullException: Value cannot be null. (Parameter 'provider')
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Provisioning.Handlers.CustomerCreatedHandler.Reauthenticate(Guid customerId) in /src/Provisioning/Handlers/CustomerCreatedHandler.cs:line 33

Answer 1

You can resolve the IMessageSession from IServiceProvider as shown here in the background worker.