HTTP Request Decorators

Decorators allow you to modify every outgoing HTTP request before it is sent. Common use cases include adding authentication tokens, injecting device information headers, or appending correlation IDs.

What Are Decorators?

An HTTP request decorator implements IHttpRequestDecorator and runs against every HTTP request made through the Mediator HTTP extension. This is different from middleware - decorators operate on the raw HttpRequestMessage rather than the mediator pipeline.

Decorators apply to all HTTP requests made through the Mediator HTTP extension.

IHttpRequestDecorator Interface

public interface IHttpRequestDecorator
{
    Task Decorate(HttpRequestMessage httpMessage, IMediatorContext context);
}

The Decorate method receives:

httpMessage - The outgoing HttpRequestMessage you can modify (add headers, set auth, etc.)
context - The mediator context containing the original request contract and any context values

Authentication Decorator

A common scenario is refreshing an access token and adding it to the request:

public class AuthHttpRequestDecorator(IAuthService authService) : IHttpRequestDecorator
{
    public async Task Decorate(HttpRequestMessage httpMessage, IMediatorContext context)
    {
        // Refresh token if expired
        if (authService.TokenExpiry < DateTimeOffset.UtcNow)
            await authService.RefreshToken();

        httpMessage.Headers.Authorization = new AuthenticationHeaderValue(
            "Bearer",
            authService.AccessToken
        );
    }
}

Device/App Info Decorator

The Shiny.Mediator.Maui package includes a built-in decorator that adds device and app information headers. Here’s a similar example showing the pattern:

public class MauiHttpRequestDecorator(
    IConfiguration configuration,
    IAppInfo appInfo,
    IDeviceInfo deviceInfo,
    IGeolocation geolocation
) : IHttpRequestDecorator
{
    public async Task Decorate(HttpRequestMessage httpMessage, IMediatorContext context)
    {
        httpMessage.Headers.Add("AppId", appInfo.PackageName);
        httpMessage.Headers.Add("AppVersion", appInfo.Version.ToString());
        httpMessage.Headers.Add("DeviceManufacturer", deviceInfo.Manufacturer);
        httpMessage.Headers.Add("DeviceModel", deviceInfo.Model);
        httpMessage.Headers.Add("DevicePlatform", deviceInfo.Platform.ToString());
        httpMessage.Headers.Add("DeviceVersion", deviceInfo.Version.ToString());
        httpMessage.Headers.AcceptLanguage.Add(
            new StringWithQualityHeaderValue(CultureInfo.CurrentCulture.Name)
        );

        if (configuration["Mediator:Http:GpsHeader"] == "true")
        {
            var gps = await geolocation.GetLastKnownLocationAsync();
            if (gps != null)
                httpMessage.Headers.Add("GpsCoords", $"{gps.Latitude},{gps.Longitude}");
        }
    }
}

Common Decorator Patterns

API Key Injection

public class ApiKeyDecorator(IConfiguration config) : IHttpRequestDecorator
{
    public Task Decorate(HttpRequestMessage httpMessage, IMediatorContext context)
    {
        var apiKey = config["ApiKey"];
        httpMessage.Headers.Add("X-Api-Key", apiKey);
        return Task.CompletedTask;
    }
}

Correlation ID

public class CorrelationIdDecorator : IHttpRequestDecorator
{
    public Task Decorate(HttpRequestMessage httpMessage, IMediatorContext context)
    {
        httpMessage.Headers.Add("X-Correlation-Id", Guid.NewGuid().ToString());
        return Task.CompletedTask;
    }
}

Locale Header

public class LocaleDecorator : IHttpRequestDecorator
{
    public Task Decorate(HttpRequestMessage httpMessage, IMediatorContext context)
    {
        httpMessage.Headers.AcceptLanguage.Add(
            new StringWithQualityHeaderValue(CultureInfo.CurrentCulture.Name)
        );
        return Task.CompletedTask;
    }
}

Multiple Decorators

You can register multiple decorators and they will all run on every HTTP request. Register them with dependency injection:

services.AddSingletonAsImplementedInterfaces<AuthHttpRequestDecorator>();
services.AddSingletonAsImplementedInterfaces<CorrelationIdDecorator>();
services.AddSingletonAsImplementedInterfaces<LocaleDecorator>();