You can easily build your own interface using the SFTPGo REST API. Anyway, SFTPGo also provides a basic built-in web interface that allows you to manage users, virtual folders, admins and connections.
With the default httpd configuration, the web admin is available at the following URL:
http://127.0.0.1:8080/web/admin
If no admin user is found within the data provider, typically after the initial installation, SFTPGo will ask you to create the first admin. You can also pre-create an admin user by loading initial data or by enabling the create_default_admin configuration key. Please take a look here for more details.
The web interface can be configured over HTTPS and to require mutual TLS authentication in addition to administrator credentials.