On ASa, you can use the following command to permit simultaneous login
vpn-simultaneous-logins
To configure the number of simultaneous logins permitted for a user, use the vpn-simultaneous-logins command in group-policy configuration mode or username configuration mode. To remove the attribute from the running configuration, use the no form of this command. This option allows inheritance of a value from another group policy. Enter 0 to disable login and prevent user access.