e.g i create a user “student” on controller-node/master and i try this command “ansible all -m ping” its not working

i get this error:

node1 | UNREACHABLE! => {
“changed”: false,
“msg”: “Failed to connect to the host via ssh: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).”,
“unreachable”: true
}

node1 is target/slave machine