// if validate is true, an error is returned if the user does not exist.
func getUserWithProvider(ctx context.Context, userProvider, user string, validate bool) (string, error) {
	switch userProvider {
	case madmin.BuiltinProvider:
		if validate {
			if _, ok := globalIAMSys.GetUser(ctx, user); !ok {
				return "", errNoSuchUser
			}
		}
		return user, nil

		return
	}

	userProvider := mux.Vars(r)["userProvider"]

	user := r.Form.Get("user")
	tokenRevokeType := r.Form.Get("tokenRevokeType")
	fullRevoke := r.Form.Get("fullRevoke") == "true"
	isTokenSelfRevoke := user == ""
	if !isTokenSelfRevoke {
		var err error
		user, err = getUserWithProvider(ctx, userProvider, user, false)
		if err != nil {