This might end up having to go to SCOTUS.
Trump needs to be certified the winner legally.
EDIT
Before you rag about SCOTUS compromised:
Why is the current ending the current ending? Is it a coincidence that it comes down to this? Are we certain their rejection of the case wasn't pre-planned?
Is there any law that prevents the taking of the oath ahead of time? Rutherford B. Hayes reportedly took the oath early. One way or another, Trump's first term ends on January 20th. What stops the presidency from transferring to Biden, with or without an inauguration ceremony?