I can't find the python file to create the rpc credentials. According to the documentation it should reside somewhere here:
using the output from the script in share/rpcauth/rpcauth.py
The python file is not provided if you installed bitcoind through PPA.
You can download it yourself
wget https://raw.githubusercontent.com/bitcoin/bitcoin/master/share/rpcauth/rpcauth.py
And run the program as follows
python3 rpcauth.py myusername mysecretpassword