# Routing

### MVC Filters

MVC action filters can be set up to conditionally execute based on the state of a feature. This is done by registering MVC filters in a feature aware manner. The feature management pipeline supports async MVC Action filters, which implement `IAsyncActionFilter`.

```csharp
services.AddMvc(o => 
{
    o.Filters.AddForFeature<SomeMvcFilter>(nameof(MyFeatureFlags.FeatureV));
});
```

The code above adds an MVC filter named `SomeMvcFilter`. This filter is only triggered within the MVC pipeline if the feature it specifies, "FeatureV", is enabled.

### Conditional Middleware

Middleware can be conditionally executed by the use of feature flags

```csharp
app.UseMiddlewareForFeature<ReferralTrackingMiddleware>("ReferralTracking");
```

With the above call, the application adds a middleware component that only appears in the request pipeline if the feature `ReferralTracking` is enabled. If the feature is enabled/disabled during runtime, the middleware pipeline can be changed dynamically.

This builds off the more generic capability to branch the entire application based on a feature.

```csharp
app.UseForFeature("featureName", appBuilder => 
{
    appBuilder.UseMiddleware<T>();
});
```


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