Well – not really new – but redesigned.
IdentityServer4 has two diagnostics facilities – logging and events. While logging is more like low level “printf” style – events represent higher level information about certain logical operations in IdentityServer (think Windows security event log).
Events are structured data and include event IDs, success/failure information activity IDs, IP addresses, categories and event specific details. This makes it easy to query and analyze them and extract useful information that can be used for further processing.
Find more details in our docs.