set_secure_random_alphanum $cspNonce 32;
# usage 
#<script nonce="**CSP_NONCE**">
# 
# sub filter to ensure that the CSP NONCE is introduce

add_header Content-Security-Policy "default-src 'none'; img-src 'self'; \
    script-src 'self' 'nonce-$cspNonce'; style-src 'self' 'unsafe-inline'; \
    font-src 'self'; base-uri 'self'; form-action 'self';\
     connect-src 'self'; frame-ancestors 'none'";
add_header X-Content-Type-Options nosniff;
add_header X-Frame-Options DENY;
add_header X-XSS-Protection "1; mode=block" always;
add_header Referrer-Policy "strict-origin";
add_header Strict-Transport-Security "max-age=31536000" always;

#sub_filter_once off;
#sub_filter_types text/html; # or *
#sub_filter **CSP_NONCE** $cspNonce;