Preserve response headers in nginx - nginx

Question

I have a reverse-proxy setup(I think), for gunicorn running a falcon app. I was also able to setup SSL on the nginx server. The /etc/nginx/nginx.conf:
worker_processes 1;
user nobody nogroup;
pid /tmp/nginx.pid;
error_log /tmp/nginx.error.log;
events {
worker_connections 1024; # increase if you have lots of clients
accept_mutex off; # set to 'on' if nginx worker_processes > 1
}
http {
include mime.types;
# fallback in case we can't determine a type
default_type application/json;
access_log /tmp/nginx.access.log combined;
sendfile on;
gzip on;
gzip_http_version 1.0;
gzip_proxied any;
gzip_min_length 500;
gzip_disable "MSIE [1-6]\.";
gzip_types application/json;
upstream app_server {
# fail_timeout=0 means we always retry an upstream even if it failed
# to return a good HTTP response
server 127.0.0.1:6789 fail_timeout=0;
}
server {
# if no Host match, close the connection to prevent host spoofing
listen 80 default_server;
return 444;
}
server {
listen 443 ssl;
client_max_body_size 4G;
# set the correct host(s) for your site
server_name 0.0.0.0;
ssl_certificate /etc/nginx/ssl/nginx.crt;
ssl_certificate_key /etc/nginx/ssl/nginx.key;
keepalive_timeout 2;
location / {
proxy_bind $server_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto https;
proxy_set_header Host $http_host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-Host $server_name;
proxy_redirect off;
proxy_pass http://app_server;
}
}
}
What do I need to change so that the response headers from gunicorn are preserved? Also, I am completely new to this. So is there anything that I should change?