Все, разобрался, получилось так
location / {
location ~ [^/]\.ph(p\d*|tml)$ {
try_files /does_not_exists @apacheback;
}
location ~* ^.+\.(gif|svg|js|css|mp3|ogg|mpe?g|avi|zip|gz|bz2?|rar|swf|woff|woff2|ico|ttf|eot|otf|flv)$ {
try_files $uri $uri/ @fallback;
expires 365d;
}
location ~* ^.+\.(jpg|jpeg|png)$ {
set $ax 0;
if ( $http_accept ~* "webp" ) {
set $ax 1;
}
if ( -e $root_path/webp$uri ){
set $ax "${ax}1";
}
if ($http_cookie ~* "modx_admin" ) {
set $ax 0;
}
if ( $ax = "11" ) {
rewrite ^ /webp$uri last;
return 403;
}
expires 365d;
try_files $uri $uri/ @fallback;
}
location ^~ /webp/ {
types { } default_type "image/webp";
add_header Vary Accept;
expires 365d;
try_files $uri $uri/ @fallback;
}
location / {
try_files /does_not_exists @fallback;
}
}