Create a self-signed SSL certificate for localhost.

mkcert.sh

brew install mkcert

function ssl-check() {
    f=~/.localhost_ssl;
    ssl_crt=$f/server.crt
    ssl_key=$f/server.key
    b=$(tput bold)
    c=$(tput sgr0)

    # local_ip=$(ip route get 8.8.4.4 | head -1 | awk '{print $7}') # Linux Version
    local_ip=$(ipconfig getifaddr $(route get default | grep interface | awk '{print $2}')) # Mac Version
    # local_ip=999.999.999 # (uncomment for testing)

    domains=(
        "localhost"
        "$local_ip"
    )

    if [[ ! -f $ssl_crt ]]; then
        echo -e "\n🛑  ${b}Couldn't find a Slate SSL certificate:${c}"
        make_key=true
    elif [[ ! $(openssl x509 -noout -text -in $ssl_crt | grep $local_ip) ]]; then
        echo -e "\n🛑  ${b}Your IP Address has changed:${c}"
        make_key=true
    else
        echo -e "\n✅  ${b}Your IP address is still the same.${c}"
    fi

    if [[ $make_key == true ]]; then
        echo -e "Generating a new Slate SSL certificate...\n"
        count=$(( ${#domains[@]} - 1))
        mkcert ${domains[@]}

        # Create Slate's default certificate directory, if it doesn't exist
        test ! -d $f && mkdir $f

        # It appears mkcert bases its filenames off the number of domains passed after the first one.
        # This script predicts that filename, so it can copy it to Slate's default location.
        if [[ $count = 0 ]]; then
            mv ./localhost.pem $ssl_crt
            mv ./localhost-key.pem $ssl_key
        else
            mv ./localhost+$count.pem $ssl_crt
            mv ./localhost+$count-key.pem $ssl_key
        fi
    fi
}

ssl-check

# If you get SSL errors later is most likely because your local IP has changed
# and the self-signed SSL certificate you created is no longer valid. 
# To remove these warnings and errors, simply repeat steps 2 and 3 above to 
# regenerate a new self-signed certificate.