Hi Xuan,
If the user will call the service provider directly via the browser using a link, the the authentication will be redirected to the Identity Provider and the user will be prompted by the Identity Provider to authenticate with his UserID and password and also to provide as a second authentication step a valid passcode (generated by the SAP Authenticator).
If there is a proper configuration on the logon page (there is an OTP Custom UI available to configure), the user will be provided with a link to the SAP Authenticator (only on mobile devices) and will be able to click on it and will get the same authentication experience as if he would have started via the SAP Authenticator from the very beginning.
See the attached screenshot from my mobile device: 
Best regards,
Donka Dimitrova