We've been promoting the new SDKs (.NET, NodeJS/TypeScript) which have been using OAuth v2 from the start.
If you're still using the old SDKs and not migrated to OAuth v2, you don't have much time left: Important Update: Authentication v1 Deprecation Extended to April 30th, 2024 – Act Now!
The latest versions of the old SDKs have been migrated to OAuth v2 so at least you'd need to update your application to use them.
.NET:
Autodesk.Forge: 1.9.9
Autodesk.Forge.DesignAutomation: 5.1.2 (uses Autodesk.Forge.Core 3.0.2 for authentication)
NodeJS:
forge-apis: 0.9.9
If you want to make absolutely sure that the SDK you're using is in fact calling the OAuth v2 endpoints, you can use a proxy utility like e.g. Charles - see picture on top.