UserHostAddressSetterHandler.cs

public class UserHostAddressSetterHandler : DelegatingHandler {

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {

        request.Properties[ApiCommonRequestKeys.UserHostAddressKey] = request.GetUserHostAddress();
        return base.SendAsync(request, cancellationToken);
    }
}

internal static class HttpRequestMessageExtensions {

    internal static HttpContextBase GetHttpContext(this HttpRequestMessage request) {

        return (HttpContextBase)request.Properties[Constants.MS_HttpContextKey];
    }

    internal static string GetUserHostAddress(this HttpRequestMessage request) {

        return request.GetHttpContext().Request.UserHostAddress;
    }
}