Alfresco Community provides several Authentication mechanisms (NTLM, LDAP, SAML...) that may be relying on different Identity Service products.
Alfresco Identity Service is a customization of Keycloak, to support some of these Authentication mechanism.
Sample Docker Compose deployment project is available in https://github.com/aborroy/alfresco-community-aims
This project includes a sample Keycloak configuration for Alfresco Realm in a JSON file, but Keycloak configuration can be also provided using the Admin Web Console.
Since the project uses a simple authorization integration, additional instructions are available in Alfresco Docs Tutorial page to configure mechanisms like SAML, LDAP or Kerberos.
In additional, following the past Alfresco TTL #133 delivered by @afaust, Community alfresco-keycloak addon describes advanced uses of Keycloak with Alfresco Platform in https://github.com/Acosix/alfresco-keycloak