cert파일 생성

creating SSL certificate
# Install mkcert tool
$brew install mkcert

# Install nss (only needed if you use Firefox)
$brew install nss

# Setup mkcert on your machine (creates a CA)
$mkcert -install

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# Create .cert directory if it doesn't exist
mkdir -p .cert

# Generate the certificate (ran from the root of this project)
mkcert -key-file ./.cert/key.pem -cert-file ./.cert/cert.pem "localhost"
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$npx create-react-app appname 

$npm start