In the Configuration > Users > Authentification module, click on Add a method or Enable a method (according to the version installed on the SNS firewall) and select Temporary accounts.
You can set a default validity period (expressed in days) when creating a new account. Every time a new account is created, this period will be suggested by default and can be replaced with a customized duration.
Apply changes. The Temporary accounts method will then be automatically added to the list of available authentication methods.