Hello,
in v1, useXForwardedFor is an option of the whitelisting system:
in v2, the whitelisting system is a middleware:
- https://docs.traefik.io/v2.1/middlewares/ipwhitelist/#ipstrategy
- https://docs.traefik.io/v2.1/middlewares/overview/
Note, in v1 the X-Forwarded-* headers are "trusted" by default, but in v2 they are not "trusted" by default, because it can be a security issue.