Ssh from linux into mac – permission denied

I'm running a Oracle Linux VM on a Windows 7 host and I'm trying to ssh into my MacBook.

I've already created the private/pub keys in my Mac. I have copied the id_rsa.pub contents into the authorized_keys file in .ssh folder.
I have changed the authorized_keys permissions to 600 for the current user.
Permissions for ~ and ~/.ssh have been changed to 700.

I have also copied the id_rsa.pub contents from the Oracle Linux VM to the authorized_keys file using

ssh-copy-id

In my Mac I also have an Oracle Linux VM into which I can ssh perfectly fine from the Oracle Linux VM in the Windows machine.

However, I cannot ssh into my Mac using just: ssh macdomain

I have to use: ssh username@macdomain to ssh successfully. Without the username it will ask me for a password and eventually result in:

Permission denied (publickey, keyboard-interactive)

This is my sshd_config file:

#   $OpenBSD: sshd_config,v 1.81 2009/10/08 14:03:41 markus Exp $

# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.

# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin

# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options change a
# default value.

#Port 22
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

# The default requires explicit activation of protocol 1
#Protocol 2

# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key

# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 1024

# Logging
# obsoletes QuietMode and FascistLogging
SyslogFacility AUTHPRIV
#LogLevel INFO

# Authentication:

#LoginGraceTime 2m
#PermitRootLogin yes
#StrictModes no
#MaxAuthTries 6
#MaxSessions 10

#RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile  .ssh/authorized_keys
AllowUsers username
# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no
# similar for protocol version 2
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# RhostsRSAAuthentication and HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes

# To disable tunneled clear text passwords both PasswordAuthentication and
# ChallengeResponseAuthentication must be set to "no".
#PasswordAuthentication no
#PermitEmptyPasswords no

# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
#GSSAPIStrictAcceptorCheck yes
#GSSAPIKeyExchange no

# Set this to 'yes' to enable PAM authentication, account processing, 
# and session processing. If this is enabled, PAM authentication will 
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
# Also, PAM will deny null passwords by default.  If you need to allow
# null passwords, add the " nullok" option to the end of the
# securityserver.so line in /etc/pam.d/sshd.
#UsePAM yes

#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
#X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#UseLogin no
#UsePrivilegeSeparation yes
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
#UseDNS yes
#PidFile /var/run/sshd.pid
#MaxStartups 10
#PermitTunnel no
#ChrootDirectory none

# pass locale information
AcceptEnv LANG LC_*

# no default banner path
#Banner none

# override default of no subsystems
Subsystem   sftp    /usr/libexec/sftp-server

# Example of overriding settings on a per-user basis
#Match User anoncvs
#   X11Forwarding no
#   AllowTcpForwarding no
#   ForceCommand cvs server

# XAuthLocation added by XQuartz (http://xquartz.macosforge.org)
XAuthLocation /opt/X11/bin/xauth

I've googled and had a look at almost every relevant topic but to no avail.