https://github.com/simplesamlphp/simplesamlphp/commit/0c6a65a1e16ca1811f858b16afb1103ffaa2095a is the fix for this and I confirmed it works. I went on the SimpleSAMLphp Slack and Tim van Dijen responded to say this bug was already found and fixed but didn't make it into the 2.0.x branch.