The documentation straight away jump into the explaining credential-store types in Elytron....but What's Elytron in the first place !! There is no brief introduction or reference link for a user to understand Elytron.

https://docs.redhat.com/en/documentation/red_hat_jboss_enterprise_application_platform/8.0/html/secure_storage_of_credentials_in_jboss_eap/credentials_and_credential_stores_in_elytron