Rename WordPress login page. Replace "key=123". Based on the code from the WCEU 2016 talk by Maurizio Pelizzone.

.htaccess

# BEGIN Hide login page
RewriteRule ^mylogin$ https://%{SERVER_NAME}/wp-login.php?key=123&redirect_to=https://%{SERVER_NAME}/wp-admin/index.php [L]

RewriteCond %{HTTP_REFERER} !^https://%{SERVER_NAME}/wp-admin
RewriteCond %{HTTP_REFERER} !^https://%{SERVER_NAME}/wp-login.php
RewriteCond %{HTTP_REFERER} !^https://%{SERVER_NAME}/login
RewriteCond %{QUERY_STRING} !^key=123
RewriteCond %{QUERY_STRING} !^action=logout
RewriteCond %{QUERY_STRING} !^action=lostpassword
RewriteCond %{REQUEST_METHOD} !POST
# END Hide login page