This problem is best directed to the Odysseus folks who maintain the ATHENA repository.
I successfully logged into ATHENA on Friday, March 25, 2022 and requested a batch of vocabularies for download.
As you all know, it takes some time for ATHENA to generate the .zip download file. So I logged out and returned to ATHENA on Sunday, March 27, 2022.
When attempting to log back in, I received the following error message:
I hope this outage is just transient, with access to the upstream “SSO” server coming back online soon. But perhaps someone from Odysseus can confirm?