Reference:
Splunk authentication: Provides Admin, Power and User by default, and you can define your own roles using a list of capabilities. If you have an Enterprise license, Splunk authentication is enabled by default. See Set up user authentication with Splunk's built-in system for more information. LDAP: Splunk Enterprise supports authentication with its internal authentication services or your existing LDAP server. See Set up user authentication with LDAP for more information. Scripted authentication API: Use scripted authentication to integrate Splunk authentication with an external authentication system, such as RADIUS or PAM. See Set up user authentication with external systems for more information. Note: Authentication, including native authentication, LDAP, and scripted authentication, is not available in Splunk Free.