About Internal authentication 

Internal authentication is based on Cassandra-controlled roles and passwords.

Like many databases, Cassandra uses rolenames and passwords for internal authentication. Role-based authentication encompasses both users and roles to bring a number of useful features to authorization. Roles can represent either actual individual users or roles that those users have in administering and accessing the Cassandra cluster.

Roles assigned to individuals and functions
For example, a user named alice is created and given login privileges:
CREATE ROLE alice WITH PASSWORD = 'enjoyLife' AND LOGIN = true;
Note that the user is created as a role and this user can log into the database with the assigned password credentials. Roles can be created with superuser, non-superuser, and login privileges. Superuser privileges allow a role to perform any database operations. Next, we create a role that will have be given access to all the functionality of a particular keyspace:
CREATE ROLE cycling_admin WITH PASSWORD = '1234abcd';
GRANT ALL PERMISSIONS ON KEYSPACE cycling TO cycling_admin;
This role, when assigned to a user, will provide certain privileges to the user based on the role's privileges; the role that is granted this role will inherit the cycling_admin privileges. The cycling_admin role is granted all permissions on the keyspace cycling in the second command. When alice is granted the role cycling_admin, alice is now granted all permissions on the keyspace cycling:
GRANT cycling_admin TO alice;
An individual user can be granted any number of roles, just as any functional role can be granted another role's permissions. In this example, the role cycling_analyst has the ability to select data, and then gains the ability to select data in the another table hockey when the role hockey_analyst is granted.
CREATE ROLE cycling_analyst WITH PASSWORD = 'zyxw9876';
GRANT SELECT ON TABLE cycling.analysis TO cycling_analyst;
CREATE ROLE hockey_analyst WITH PASSWORD = 'Iget2seeAll';
GRANT SELECT ON TABLE hockey.analysis TO hockey_analyst;
GRANT hockey_analyst TO cycling_analyst;
GRANT cyclist_analyst TO jane;
If a user then is granted the role of cycling_analyst role, that user will be able to select data in the additional table hockey The illustration above would be modified to show that the user jane now has access to two tables.
Note: Permissions and SUPERUSER status are inherited, but the LOGIN privilege is not.
An important change that roles-based access control also introduces is that the need for SUPERUSER privileges in order to perform user/role management operations is removed. A role can be authorized to create roles or be authorized to grant and revoke permissions:
// Give cycling_accounts the right to create roles
GRANT CREATE ON ALL ROLES TO cycling_accounts;
// Give cycling_accounts the right to grant or revoke permissions
GRANT AUTHORIZE ON KEYSPACE cycling TO cycling_accounts;
GRANT cyclist_accounts TO jane;
GRANT cyclist_accounts TO john;
Internal authentication and authorization information is stored in the following Cassandra tables:
system_auth.roles
Table that stores the role name, whether the role can be used for login, whether the role is a superuser, what other roles the role may be a member of, and a bcrypt salted hash password for the role.
system_auth.role_members
Table that stores the roles and role members.
system_auth.role_permissions
Table that stores the role, a resource (keyspace, table), and the permission that the role has to access the resource.
system_auth.recqlshSourceole_permissons_index
Table that stores the role and a resource that the role has a set permission.
Cassandra is configured with a default superuser role and password pair of cassandra/cassandra by default. Using this role, additional roles can be created using CQL commands. To secure the system, this default role should be deleted once a non-default superuser has been created.

Once roles and passwords have been set, Cassandra can be configured to use authentication in the cassandra.yaml file.

The location of the cassandra.yaml file depends on the type of installation:
Package installations /etc/cassandra/cassandra.yaml
Tarball installations install_location/resources/cassandra/conf/cassandra.yaml

If roles exist and Cassandra is configured to use authentication, Cassandra tools must be executed with optional authentication options.