That depends on your application. If SSO was triggered by a user clicking a button, the button click event would call GetStatusAsync().IsSsoCompletionPending() to check if there’s a pending SSO and if there is it would most likely do nothing. Alternatively, it could display a message saying SSO is in progress.
Normally once the SSO flow starts, control will be immediately passed to the IdP’s website so the user won’t have an opportunity to initiate SSO again. However, it can occur if they use the back button etc.