docker-ftps/rootfs/app/cert-init.sh

#!/bin/sh

############ TLS
TLS_CERT=${TLS_CERT:-/certs/cert.pem}
TLS_KEY=${TLS_KEY:-/certs/privkey.pem}
TLS_CHAIN=${TLS_CHAIN:-/certs/chain.pem}

cat "$TLS_CERT" > /etc/proftpd/cert.pem
cat "$TLS_KEY" > /etc/proftpd/privkey.pem
cat "$TLS_CHAIN "> /etc/proftpd/chain.pem

############ CHECK CERT KEY ALGO
ALGO=$(openssl x509 -in /etc/proftpd/cert.pem -text | sed -n 's/\ *Public Key Algorithm: //p' | tr '\n')

############ UPDATE cert config if needed
if [ "$ALGO" = "id-ecPublicKey" ] ; then
cat > /etc/proftpd/conf.d/certificate.conf <<EOF
<IfModule mod_tls.c>
  TLSECCertificateFile                    /etc/proftpd/cert.pem
  TLSECCertificateKeyFile                 /etc/proftpd/privkey.pem
  TLSCertificateChainFile                 /etc/proftpd/chain.pem
</IfModule>
EOF
fi

if [ "$ALGO" = "rsaEncryption" ] ; then
cat > /etc/proftpd/conf.d/certificate.conf <<EOF
<IfModule mod_tls.c>
  TLSRSACertificateFile                    /etc/proftpd/cert.pem
  TLSRSACertificateKeyFile                 /etc/proftpd/privkey.pem
  TLSCertificateChainFile                  /etc/proftpd/chain.pem
</IfModule>
EOF
fi

md5sum "$TLS_CERT" > /app/sums
echo "Certificate ready"