Salesforce announced that beginning 1st February 2022, customers are contractually required to use multi-factor authentication (MFA) when accessing Salesforce products.
The MFA requirement, however, does not apply to all user, login and environment types, as detailed in this FAQ. Specifically, the MFA requirement does not apply to API logins. Since our applications access Salesforce via the API, the new MFA requirement does not impact our applications.