The self service portal (https://idp-portal.suse.com) seems to be stable again.
Background story:
Server errors were caused by the database connection slots having filled up. We found the system creates one database connection per login attempt and takes a while to close the connections again - due to the relatively low number of maximum allowed connections by the backend database we concluded someone on the internet caused a denial of service by attempting to log in too often. We raised the issue with the software vendor, who advised us on tuning the backend database to mitigate such issues in the future. An internal task tracking the implementation of the suggested changes has been filed. To prevent DOS by bots we asked the vendor about the implementation of a Captcha system, which would block such login attempts even before a database query is initiated - however the vendor is not planning to work on such a feature in the near future.