Share same session with multiple domain using nginx & tomcat - session

Question

We've a running a grails application on a tomcat server behind nginx for multiple subdomain:
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;
log_format main '$remote_addr - $remote_user [$time_local] "$tempRequest" '
'$status $body_bytes_sent "$http_referer" '
'"$http_user_agent" "$http_x_forwarded_for" \n';
access_log /var/log/nginx/access.log main;
sendfile on;
#tcp_nopush on;
keepalive_timeout 65;
gzip on;
gzip_http_version 1.1;
gzip_min_length 1000;
gzip_buffers 16 8k;
gzip_disable "MSIE [1-6] \.";
gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript application/javascript text/x-js;
gzip_vary on;
upstream main {
server localhost:8081;
}
include /etc/nginx/conf.d/*.conf;
# First server config to listen top level domain request (https/http) & redirect to mnop.com
server {
listen 80;
listen 443 ssl;
server_name xyz.com www.xyz.com;
ssl_certificate /etc/nginx/server.crt;
ssl_certificate_key /etc/nginx/server.key;
return 301 https://mnop.com;
}
# Second server config to redirect all non https requests to https request.
server {
listen 80;
# Remember wildcard domain with "*" doesn't listen top level domain.
# Hence no conflict with first server config.
server_name *.xyz.com;
rewrite ^ https://$host$request_uri? permanent;
}
# Third server config to listen https request & serves all html with nginx.
server {
listen 443 ssl;
server_name *.xyz.com;
ssl on;
ssl_certificate /etc/nginx/server.crt;
ssl_certificate_key /etc/nginx/server.key;
ssl_protocols SSLv3 TLSv1 TLSv1.1 TLSv1.2;
ssl_ciphers HIGH:!aNULL:!MD5;
ssl_session_cache shared:SSL:10m;
location / {
set $tempRequest $request;
if ($tempRequest ~ (.*)j_password=[^&]*(.*)) {
# Mask spring authentication password param.
set $tempRequest $1j_password=****$2;
}
proxy_set_header Host $http_host;
proxy_set_header X-Forwarded-Host $host;
proxy_set_header X-Forwarded-Server $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://main;
proxy_redirect http://$host https://$host;
}
location /ng/app {
root /usr/share/apache-tomcat-7.0.54/webapps/ROOT;
}
}
}
A tomcat app is running on port 8081 and any subdomain like: a.xyz.com or b.xyz.com, working fine and sharing same session.
But We need to use the same session and app using a different domain like: abc.com, how can I achieve that? I tried setting virtual hosts and proxy_cookie_domain but nothing worked?