At this time, Saxo Bank only offers Certificate-Based Authentication to institutional partners (see here for details).
Individual/Corporate direct retail clients of Saxo Bank and its subsidiaries cannot request CBA access to their accounts, primarily because of compliance reasons. As a regulated entity, Saxo Bank is required to display (and confirm) a number of (regional) disclaimers upon logon, such as the MiFID appropriateness questionnaire/results for EU residents. The current implementation therefore requires manual logon, as these disclaimers are shown to the end-user before authorization is granted to the account.
Once authorization has been granted however, the provided access and refresh tokens can be used to keep the session active for as long as the client app requires. Under certain rare circumstances such as changes to the approved disclaimers (which requires re-confirmation), existing sessions can be terminated by OpenAPI. For optimal stability, authenticate your app with Saxo Bank at least once per week (typically before markets open on Monday) to ensure uninterrupted, consistent authorization with OpenAPI.