Acl not working!

curl -X POST localhost:8080/login -d ‘{
“userid”: “groot”,
“password”: “password”

this command not working in terminal
it gives error
{“errors”:[{“message”:“Authentication from address failed: while querying user with id groot: : Attribute dgraph.xid is not indexed.”,“extensions”:{“code”:“ErrorInvalidRequest”}}],“data”:null}

how to solve this? Do i need a dgraph contract for working with ACL.??

This is being discussed at

dgraph alpha --my=localhost:7080 --lru_mb=1024 --zero=localhost:5080 --logtostderr -v=3 --acl_secret_file ./hmac-secret

not able to run this command?
It is giving me the following error!
where should be my hmac-secret file?