We removed the org.bouncycastle module for 38 Beta1 but this broke the Keycloak SAML adapter feature pack:

https://github.com/keycloak/keycloak/blob/26.4.0/distribution/galleon-feature-packs/saml-adapter-galleon-pack/src/main/resources/modules/system/add-ons/keycloak/org/keycloak/keycloak-common/main/module.xml

So we need to revert that until we get a release of that FP with that corrected.