RPC auth for bitcoind
Bitcoin Core is moving your configuration away from a user/pass.
Passing a username and password directly to Bitcoin Core is a deprecated mode, and Bitcoin Core has a couple of possible replacements for how to stop using the rpcuser and rpcpass.
The easy one to start using with lnd is rpcauth.
You can do that by getting this python script and executing it like: ./rpcauth.py rpcuser
Running this will show: "String to be appended to bitcoin.conf"