FortiGate supports both pre-shared key and certificate signature methods for IKEv1 authentication. These methods provide flexibility depending on the security requirements of the network. Additionally, FortiGate supports Extended Authentication (XAuth), which requests a username and password from the remote peer, enhancing security by adding an extra layer of authentication. The XAuth method does not necessarily make the authentication faster; it is an additional security measure.
Reference:
FortiOS 7.4.1 Administration Guide: IPsec VPN Configuration