How to configure two-way certificate verification on nginx proxy server

#!/bin/bash -x
set -e
for C in `echo root-ca intermediate`; do
 mkdir $C
 cd $C
 mkdir certs crl newcerts private
 cd ..
 echo 1000 > $C/serial
 touch $C/index.txt $C/index.txt.attr
 echo '
[ ca ]
default_ca = CA_default
[ CA_default ]
dir = '$C' # Where everything is kept
certs = $dir/certs # Where the issued certs are kept
crl_dir = $dir/crl # Where the issued crl are kept
database = $dir/index.txt # database index file.
new_certs_dir = $dir/newcerts # default place for new certs.
certificate = $dir/cacert.pem # The CA certificate
serial = $dir/serial # The current serial number
crl = $dir/crl.pem # The current CRL
private_key = $dir/private/ca.key.pem # The private key
RANDFILE = $dir/.rnd # private random number file
nameopt = default_ca
certopt = default_ca
policy = policy_match
default_days = 365
default_md = sha256
[ policy_match ]
countryName = optional
stateOrProvinceName = optional
organizationName = optional
organizationalUnitName = optional
commonName = supplied
emailAddress = optional
[req]
req_extensions = v3_req
distinguished_name = req_distinguished_name
[req_distinguished_name]
[v3_req]
basicConstraints = CA:TRUE
' > $C/openssl.conf
done
openssl genrsa -out root-ca/private/ca.key 2048
openssl req -config root-ca/openssl.conf -new -x509 -days 3650 -key root-ca/private/ca.key -sha256 -extensions v3_req -out root-ca/certs/ca.crt -subj '/CN=Root-ca'
openssl genrsa -out intermediate/private/intermediate.key 2048
openssl req -config intermediate/openssl.conf -sha256 -new -key intermediate/private/intermediate.key -out intermediate/certs/intermediate.csr -subj '/CN=localhost.'
openssl ca -batch -config root-ca/openssl.conf -keyfile root-ca/private/ca.key -cert root-ca/certs/ca.crt -extensions v3_req -notext -md sha256 -in intermediate/certs/intermediate.csr -out intermediate/certs/intermediate.crt
mkdir out
for I in `seq 1 3` ; do
 openssl req -new -keyout out/$I.key -out out/$I.request -days 365 -nodes -subj "/CN=$I.example.com" -newkey rsa:2048
 openssl ca -batch -config root-ca/openssl.conf -keyfile intermediate/private/intermediate.key -cert intermediate/certs/intermediate.crt -out out/$I.crt -infiles out/$I.request
done

worker_processes 1;
events {
  worker_connections 1024;
}
stream{
  upstream backend{
    server 127.0.0.1:8080;
  }
  server {
    listen 8888 ssl;
    proxy_pass backend;
    ssl_certificate intermediate.crt;
    ssl_certificate_key intermediate.key;
    ssl_verify_depth 2;
    ssl_client_certificate root.crt;
    ssl_verify_client optional_no_ca;
  }
}

curl \
 -I \
 -vv \
 -x https://localhost:8888/ \
 --proxy-cert client1.crt \
 --proxy-key client1.key \
 --proxy-cacert ca.crt \
 https://www.baidu.com/