openresty nginx search for keyword in post request body data

I have been using openresty nginx for simple request forwarding purpose, it is working as expected, i am forwarding each incoming request to another URL using below code :

        location /app/ {
        proxy_pass      https://example.com/abc/;
        proxy_read_timeout 60s;         
        proxy_pass_header Server;
        proxy_set_header          Host            $host;
        proxy_set_header          X-Real-IP       $remote_addr;
        proxy_set_header          X-Forwarded-For $proxy_add_x_forwarded_for;
        add_header  X-Frame-Options "SAMEORIGIN" always;

and i am logging each POST request with below code :

server {
                  log_format post_logs '[$time_local] "$request" $status '  

                  '$body_bytes_sent "$http_referer" '        

                  '"$http_user_agent" [$request_body]';
      }



location /app/ {
                  access_log  logs/post.log post_logs;
               }

Now my requirement is that before forwarding each request, i want to filter post request body data for specific string/keyword , it should only forwarded to proxy URL https://example.com/abc/ if specific string/keyword is found in post data.

I did some research but did not find anything that helps me achieve this, can anyone help ?

Solution

Finally I got it done with help of lua :

location /app/ {
.
.
.
    
access_by_lua '
            ngx.req.read_body()
            local data = ngx.req.get_body_data()
            local  match = ngx.re.match(ngx.var.request_body, "<reqid>search</reqid>")                      

#local  match = ngx.re.match(ngx.var.request_body, "<reqid>search</reqid>","i") for case insensitive match          
            
            if match then
                #nothing to do
            else
                return ngx.exit(ngx.HTTP_FORBIDDEN)
            end';
            proxy_pass      https://example.com/abc/;
            
}

here request body data will be assign to variable 'data' and with use of ngx.re.match we can match string/keyword with request body data, in above example if <reqid>search</reqid> not found in request body then it will return 403 forbidden, if found then it will be passed to proxy_pass.

It can be very useful for filtering incoming request before processing it.