Way to get configured registries

[s1n7ax]

nvim-java/mason-registry provides packages like java-test 0.40.1 & openjdk-17 that's not available in main registry.

In the plugin I'm working on, I install, java-test, java-debug-adapter & openjdk-17 when lspconfig.jdtls.setup is called. Before that, I want to make sure the registry is added and updated before that. So I would like to know if there is an API to get a list of registries or updated registries. Purpose of this is to warn the user to add it if it's not available. Is this possible right now?