Transparently identify users with authentication realms - This option is available when one or more authentication realms are configured to support transparent identification using one of the following authentication servers:
Active Directory - Create an NTLM or Kerberos authentication realm and enable transparent user identification. In addition, you must deploy a separate Active Directory agent such as Cisco's Context Directory Agent. For more information, see Transparent User Identification with Active Directory.
LDAP - Create an LDAP authentication realm configured as an eDirectory, and enable transparent user identification. For more information, see Transparent User Identification with LDAP.
Details:
https://www.cisco.com/c/en/us/td/docs/security/wsa/wsa11-0/user_guide/b_WSA_UserGuide/b_WSA_UserGuide_chapter_01001.html#:~:text=Transparently%20identify%20users%20with%20authentication,User%20Identification%20with%20LDAP.

Multi-factor authentication (MFA) is an authentication method that requires the user to provide two or more verification factors to gain access to a resource such as an application, online account, or a VPN. MFA is a core component of a strong identity and access management (IAM) policy1. MFA is important to implement inside of an organization because it can prevent brute force attacks from being successful. A brute force attack is a type of cyberattack that tries to guess the user's password or PIN by trying different combinations until it finds the correct one. This can be done manually or with automated tools. MFA can stop brute force attacks by requiring an additional factor of authentication that the attacker does not have, such as a phone, a token, a biometric, or a location. MFA can also reduce the risk of other types of attacks that rely on stealing or compromising the user's credentials, such as phishing, keylogging, or credential stuffing. References := 1:
What is Multi-Factor Authentication (MFA)? | OneLogin