I'm attempting to extend the source code for a module our team purchased that targets .NET Framework 4.5.  I would like to add the DotNetNuke.WebAPI NuGet package but receive an error stating it relies upon System.Web.Http and cannot be installed.  Unfortunately, it doesn't appear that the targeted version (4.5) will support the use of Web API.  

What is the best practice approach to call a Web API from within DNN?  Is there a different DotNetNuke namespace that I should use?  The Web API that I plan to build will in turn make calls to other APIs for payment processing purposes.  These calls need to be asynchronous and I don't want our users to be delayed while they're awaiting a response from the processor API.  Can I build out a separate Web API solution targeting Core 2 that calls out to these external APIs and in turn reports the responses back to DNN?  

Greatly appreciate a nudge in the proper direction.