$ cat credentials.txt
username=admin
password=Ex67Hn*9#(jw
$ kubectl create secret generic SECRET_NAME --from-env-file ./credentials.txt

$ echo -n 'admin' > ./username.txt
$ echo -n '1f2d1e2e67df' > ./password.txt
$ kubectl create secret generic SECRET_NAME --from-file=./username.txt --from-file=./password.txt
$ kubectl create secret generic SECRET_NAME --from-file=username=./username.txt --from-file=password=./password.txt
