Not sure what was the particular issue you faced, but ASP.NET Core has come a long way – you can run .NET Core apps on Linux as well, not to mention the whole thing is open source under DotNet Foundation [0].
Is the source code for ASPSecurityKit available for review? Generally enterprises prefer that when it comes to using a security component in a critical production system.
Yes, under business/enterprise plan [0], you'll get access to the complete source code on our private GitHub repository.