The 0% Interest Rate of the Current SAVE Administrative Forbearance

What is ED Secretary Cardona's statutory basis for 0% interest during the current SAVE administrative forbearance? I can't find anything giving him the authority to set, even on a temporary basis, the interest rates for student loans. Only Congress can do that.

As a reference point, during the COVID, 0% interest rate administrative forbearance it literally took an act of Congress to set the rate on all federally-held student loans to 0%. I don't remember any sort of bickering about it because it was just so obvious that Congress needed to approve it that there wasn't even a question about it.

What has changed or what am I overlooking? Or is this just a big middle finger from Biden & Cardona towards Congress, the courts, and the Constitution?

I'm not trying to start World War III. It's just odd that nobody is talking about it.