How add "user-" prefix to the user slug on OAuth login flow?

I am login using OAuth2 with FusionAuth as the identity provider. I am using the apostrophe-passport module with a passport-fusionauth module created by me as a strategy. When the login flow ends, a user is created in Apostrophe that can be edited. I want to edit that user but in the form the created slug field does not have the “user-” prefix that is required. How to establish that when the user is created in the login flow, that field is created with that prefix?.