gistfile1.txt

$ ls -ld /home ~/.ssh ~/.ssh/authorized_keys
drwxr-xr-x 3 root root    18 Mar  2 12:56 /home
drwx------ 2 jiri users 4096 Mar 23 12:28 /home/jiri/.ssh
-rw------- 1 jiri users  109 Mar 12 16:55 /home/jiri/.ssh/authorized_keys

$ cat /tmp/ssh/sshd_config 
AllowUsers jiri
AuthorizedKeysFile      /home/jiri/.ssh/authorized_keys
Subsystem       sftp    /usr/libexec/ssh/sftp-server
Port 1234
ListenAddress 127.0.0.1
AddressFamily inet
HostKey /tmp/ssh/ssh_host_rsa_key
HostKey /tmp/ssh/ssh_host_ecdsa_key
HostKey /tmp/ssh/ssh_host_ed25519_key
PubkeyAuthentication yes
PasswordAuthentication no
ChallengeResponseAuthentication no

$ /usr/sbin/sshd -d -D -f /tmp/ssh/sshd_config
...
debug1: temporarily_use_uid: 1000/100 (e=1000/100)                                                           [23/1806]
debug1: trying public key file /home/jiri/.ssh/authorized_keys                          
debug1: fd 4 clearing O_NONBLOCK              
debug1: /home/jiri/.ssh/authorized_keys:1: matching key found: ED25519 SHA256:zb6WeEUXwWXLP5Hh7nbJRdNDPFr0xsKIOzo2yjz8
+bA                                                                                                                   
debug1: /home/jiri/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
Accepted key ED25519 SHA256:zb6WeEUXwWXLP5Hh7nbJRdNDPFr0xsKIOzo2yjz8+bA found at /home/jiri/.ssh/authorized_keys:1
debug1: restore_uid: (unprivileged)
Postponed publickey for jiri from 127.0.0.1 port 45066 ssh2 [preauth]
debug1: userauth-request for user jiri service ssh-connection method publickey [preauth]
debug1: attempt 2 failures 0 [preauth]            
debug1: temporarily_use_uid: 1000/100 (e=1000/100)
debug1: trying public key file /home/jiri/.ssh/authorized_keys
debug1: fd 4 clearing O_NONBLOCK
debug1: /home/jiri/.ssh/authorized_keys:1: matching key found: ED25519 SHA256:zb6WeEUXwWXLP5Hh7nbJRdNDPFr0xsKIOzo2yjz8
+bA
debug1: /home/jiri/.ssh/authorized_keys:1: key options: agent-forwarding port-forwarding pty user-rc x11-forwarding
Accepted key ED25519 SHA256:zb6WeEUXwWXLP5Hh7nbJRdNDPFr0xsKIOzo2yjz8+bA found at /home/jiri/.ssh/authorized_keys:1
debug1: restore_uid: (unprivileged)
debug1: auth_activate_options: setting new authentication options
Accepted publickey for jiri from 127.0.0.1 port 45066 ssh2: ED25519 SHA256:zb6WeEUXwWXLP5Hh7nbJRdNDPFr0xsKIOzo2yjz8+bA
debug1: monitor_child_preauth: jiri has been authenticated by privileged process
...