I am willing to prepare PR. I just need green light from you :)

Hey @trejjam,

Thanks for your offer! It's something I considered too, so 👍🏻

A few notes, in no particular order:

• TimeProvider can technically be used on .NET Standard 2.0/.NET Framework 4.6.2+ thanks to the package you mentioned, but since the Microsoft.Extensions/Microsoft.Bcl packages are tied to the .NET release matching their package version (i.e they have the same support policy), we'll want to use TimeProvider only on .NET 8.0+ and keep using DateTime.UtcNow/DateTimeOffset.UtcNow for the other TFMs. For that, we'll need to add a SUPPORTS_TIME_PROVIDER compilation constant in Directory.Build.targets. You can take a look at what's been done for SUPPORTS_HTTP_CLIENT_RESILIENCE for some inspiration 😃

• Retrieving TimeProvider directly from DI would work, but I'd prefer if we attached it to OpenIddict*Options and had an OpenIddict*Configuration class implementing IPostConfigureOptions<OpenIddict*Options> to resolve a default, DI-provided instance when no provider has been explicitly added (it's the pattern used in ASP.NET Core for the authentication handlers: https://github.com/dotnet/aspnetcore/blob/e8eeea60605f323014ab86ea34c2bd87ca8e84d7/src/Security/Authentication/Core/src/AuthenticationBuilder.cs#L141). DateTimeOffset.UtcNow is used in multiple projects, so we'll need to update a few options classes 😄

• DateTime.UtcNow is used in the EF 6, EF Core and MongoDB stores, but since it's used for a LINQ query that is translated to SQL, we'll want to keep using it to ensure it's correctly mapped to GETUTCDATE().

I bumped an idea for a structure: https://github.com/openiddict/openiddict-core/pull/2071/files
Can you take a look?