Automatically add SSL server certificate to list of trusted certificates during build

Dockerfile

FROM openjdk:8-jdk-alpine

ENV EMAIL_HOSTNAME="smtp.gmail.com"
ENV EMAIL_PORT="587"
RUN apk add --no-cache openssl
RUN openssl s_client -showcerts -connect $EMAIL_HOSTNAME:$EMAIL_PORT -starttls smtp </dev/null 2>/dev/null | openssl x509 -outform DER > my-certificate.der
RUN echo yes | $JAVA_HOME/bin/keytool -import -trustcacerts -file my-certificate.der -alias my-certificate -keystore $JAVA_HOME/jre/lib/security/cacerts -storepass changeit