some repositories, like https://hub.docker.com/_/registry/ (depending on configuration) and the SuSE Portus Project (https://github.com/SUSE/Portus) und some commercial offerings of the above (like https://private-docker-registry.com/) use a different authentication scheme, where the users credentials must be sent to an authentication server, which will return a (jw-) token for authentication at the registry itself.
using https://docs.docker.com/registry/spec/auth/token/ that can be resolved using basic auth
some repositories, like https://hub.docker.com/_/registry/ (depending on configuration) and the SuSE Portus Project (https://github.com/SUSE/Portus) und some commercial offerings of the above (like https://private-docker-registry.com/) use a different authentication scheme, where the users credentials must be sent to an authentication server, which will return a (jw-) token for authentication at the registry itself.