How to set up event subscription in an app

Subscribing to events

In order to receive events in the application you need create a subscription. While you can create a subscription authenticated as a user, most scenarios will probably be to authenticate as the organization owning the application, and to create the subscription as part of the startup process of the application. This example covers authenticating as an organization through maskinporten.

You should first make sure you have a client definition registered in Maskinporten for your application. See Authenticating with Maskinporten on how register a client.

Configuring Maskinporten integration

Even though we are authenticating through maskinporten, we can’t use the received token directly since Altinn Events only supports an Altinn token. To solve this we need to exchange the Maskinporten token into an Altinn token. The example below adds a message handler to the EventsSubscriptionClient used to communicate with Maskinporten. This handler automatically requests a token from Maskinporten, exchanges it to an Altinn token and adds the token to the request to the Event System when creating a subscription.

This code should be added to Program.cs.

services.AddMaskinportenHttpClient<MaskinportenClientDefinition, EventsSubscriptionClient>(
    config.GetSection("MaskinportenSettings"), clientDefinition =>
        clientDefinition.ClientSettings.Scope = "altinn:serviceowner/";
        clientDefinition.ClientSettings.ExhangeToAltinnToken = true;
    }).AddTypedClient<IEventsSubscription, EventsSubscriptionClient>();

Scope and ExchangeToAltinnToken need to be configured in code and not in AppSettings.json if you have multiple external dependencies that requires the use of Maskinporten. This is to avoid scopes belonging to one external api being sent to another api. Some api’s accept this while others will reject the request due to unknown scopes. It’s also best practice not to leak unnecessary scopes to other api’s that don’t require it to avoid token misuse.

The MaskinportenClientDefinition in the example above is a custom implementation of IClientDefinition from the nuget package Altinn.ApiClients.Maskinporten which is included as a part of the Altinn.App.Core package. If you don’t need a custom implementation you can use one of the built in client definitions.

Depending on what type of ClientDefintion you use you typically need to specify either a certificate file and password, encoded jwk, encoded x509 certificate or enterprise username/password in order to authenticate with Maskinporten in addition to the environment and client id. These can be shared between the various integrations.

  "MaskinportenSettings": {
    "Environment": "ver2",
    "ClientId": "",
    "CertificatePkcs12Path": "",
    "CertificatePkcs12Password": ""

Here is a C# class of the settings available for reference.

Protecting the event endpoint with a secret

Receving events in the application is based on exposing a webhook endpoint to which the Event Service posts the event. Upon receiving an event, the application validates if a secret is provided before accepting the event. The secret is provided by implementing the IEventSecretCodeProvider interface. By default there is an example implementation in place using a key from the key vault using a key with the name EventSubscription--SecretCode in the key vault the value of that key is used. You should hover not use the same key/value for multiple applications so it’s recomended to create your own implementation.

Note that the return url and the secret code is part of the subscription definition. This means that if you rotate the key, you should remove the existing subscription first, or else you will have two active subscriptions for the same events.

Create subscription

Once you have your client registered with Maskinporten, your config setup, your ClientDefinition in place and your webhook secret defined - you are ready to add the code required to make a subscription.

The example below is using the IHostedService from Microsoft which, in this case, run once after the services are registered in the container, but before the application is configured.

using Altinn.App.Core.Infrastructure.Clients.Events;
using Altinn.App.Core.Internal.Events;
using Altinn.App.Core.Models;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace Altinn.App.Core.EFormidling
    /// <summary>
    /// Hosted service to set up prequisites for Eformidling integration.
    /// </summary>
    public class EformidlingStartup : IHostedService
        private readonly AppIdentifier _appIdentifier;
        private readonly IEventsSubscription _eventsSubscriptionClient;
        private readonly ILogger<EformidlingStartup> _logger;

        /// <summary>
        /// Initializes a new instance of the <see cref="EformidlingStartup"/> class.
        /// </summary>
        public EformidlingStartup(AppIdentifier appId, IEventsSubscription eventsSubscriptionClient, ILogger<EformidlingStartup> logger)
            _appIdentifier = appId;
            _eventsSubscriptionClient = eventsSubscriptionClient;
            _logger = logger;

        public async Task StartAsync(CancellationToken cancellationToken)
            var eventType = "app.eformidling.reminder.checkinstancestatus";
                Subscription subscription = await _eventsSubscriptionClient.AddSubscription(_appIdentifier.Org, _appIdentifier.App, eventType);

                _logger.LogInformation("Successfully subscribed to event {eventType} for app {appIdentifier}. Subscription {subscriptionId} is being used.", eventType, _appIdentifier, subscription.Id);

            catch (Exception ex)
                _logger.LogError("Unable to subscribe to event {eventType} for app {appIdentifier}. Received exception {exceptionMessage} with {stackTrace}", eventType, _appIdentifier, ex.Message, ex.StackTrace);

        /// <inheritdoc/>
        public Task StopAsync(CancellationToken cancellationToken)
            return Task.CompletedTask;
If the hosted service fail to run succesfully, ie. throws an exception, the application will fail to start. If you don’t won’t this behavior you shold catch any exception and don’t rethrow it.