I have a Cassandra cluster running on Ubuntu. I would like to enable authentication so that not everyone will have access to the Cassandra database and run queries.
Enabling simple authentication is available at https://docs.datastax.com/en/cassandra/3.0/cassandra/configuration/secureConfigNativeAuth.html
But, I am looking for integrating Cassandra with LDAP, Active Directory
You will have to change the default authenticator from AllowAllAuthenticator to PasswordAuthenticator or some custom authenticator.
You can also enable roles for a finer grained access.
Check the following:
Later edit: since you need LDAP autentication you can use the one created by Instaclustr. Details - Apache Cassandra LDAP Authentication and the source code.