With Authentication, your clients will add an extra layer of security to their account for additional protection and security. There are two options available as below.
Force all accounts to use 2FA - this will ask clients to login using an extra layer of security. It requires an extra login credential to gain access to an account. Google authenticator and Microsoft authenticator are two options available for such a task. This is the preferred and most secure option available.
Force login before signing - this will ask clients to log into their portal account before signing a document.