US Patent 11893105 Generating and validating activation codes without data persistence

User system authentication includes a service infrastructure system receiving, from the user system, an authentication request including a user account identifier, generating a first validation code by performing a hash algorithm on the user account identifier and a first timestamp associated with the authentication request, sending to an email account associated with the user account identifier, an email message including the first validation code, receiving from the user system, a verification code, in response to receiving the verification code, generating a second timestamp, validating the second timestamp, in response to determining that the second timestamp is valid, generating a second validation code by performing the hash algorithm on the user account identifier and the first timestamp associated with the authentication request, comparing the verification code and the second validation code, and authenticating the user system, in response to a determination that the verification code and the second validation code match.