ASP.NET Unframed MVC Web API for Flex 4.6 Interface

I'm relatively new to development, so please correct me when distracted. I have a Flex 4.6 web application as a front end to the application and SQL Server 2008 R2 as a database on an IIS server. Currently, it should be used over the local network, but should be able to be carried over the Internet. I need a Flex web application solution to connect to DB without direct call from clients. To avoid this, I thought about embedding the interface using SOAP or Web API using ASP.NET. The problem is with MVC, although the solid architecture is too complex for my needs and a lot of work in case of modifications. My question is, is the web API dependent on using MVC to implement it, or can plain ASP.NET work? If it works on ASP.NET;do I still need to create models and controllers in a simple ASP.NET project? If I decide to authenticate what approaches are available that I can look into, is it effective? Any other solutions or suggestions are appreciated.