The authentication is a process of providing proof to determine the original identity of someone or something. To have access to some technologies or companies network, these proofs are needed and so the same reason is applicable with VPN as it requires many authentication methods to differentiate between the truth & fake.
Here is a brief list of different methods of which are present in VPN and for authentication method; specific authentication protocol is always used. The methods are as:-
EAP Authentication method: – EAP called as Extensible Authentication Protocol which is used to authenticate remote access connection. The remote VPN client and authenticator (ISA) decides whether to start authentication mechanism or not. In this method authentication works simultaneously by requesting for authentication information and in return responses comes from the remote VPN client.
MS CHAP AUTHENTICATION METHOD: – Microsoft Challenge Handshake authentication protocol is the full name of MS-CHAP which works after starting the authenticator challenge. Then the main purpose of the challenge to the remote access client begins by sending a session identifier along with challenge string. The client revert the same by sending the non-reversible encryption of the string. The identification also occurred along with password. After receiving all these from client, authenticator checks the credentials and permits the access after successful authentication.
UNENCRYPTED PASSWORDS (PAP):- It is used for less secure clients and does not include any encryption just uses plain text passwords.
SHIVA PASSWORD AUTHENTICATION PROTOCOL (SPAP):- This is a password authentication protocol and said as less secure as the same password is sent which was used by user before. Just they change the form in a specific way by reversing. So, just the reversible changing of the form will it not be a risk for users due to reversible encrypted form of password.