ASP.NET Core 8 Support

Support for ASP.NET Core 8 will be available for the currently shipping OpenID providers soon after the final .NET 8.0 release ships in November 2023. In the meantime, packages for ASP.NET Core 8 are available from our [MyGet feed](https://www.myget.org/gallery/aspnet-contrib) starting with version `8.0.0-preview.3.23215.59` for .NET 8 preview 3.