The LEADTOOLS SDK provides a Web-Scanning library that implements TWAIN(Windows) or SANE(Linux) scanning through .NET components implemented in a web service. The .NET components are also available as NuGet packages from nuget.org and can be used in a .NET Core project.
An online demo is available from the LEADTOOLS website here. When trying this demo, note that it searches for the scanning web service before prompting to download an installer that will set up the web service.
The toolkit also provides a JS Document Viewer which allows for the display of documents in browser through interaction with a .NET document service. An online demo for this is also available here.
The projects for the scanning web service, the JS web scanning viewer, and the JS document viewer in the demo can be found in the free evaluation of the toolkit, available from the website here.
Edit: Added Disclaimer: I work for the vendor of this toolkit.