Can we bypass user creation and role synchronization in token based external auth?

Dear Team,

We think token based external authentication is best suited for our application. However, we want to separate Authentication and User Creation logic separate. We will be creating users in Jasper report server through a utility using Rest APIs. 

Can we modify token based authentication to just authenticate the user i.e. just check if the user in the token exists in the Jasper Server database. If it exists then Authentication is successful and if it does not then fail the authentication.

Also, can you post some sample code and configuration if possible.

Any help in this regard will be greatly appreciated.

Thank you.