#!/bin/bash
#
# Obtaining Apple Push Notification Services certificates:
#
# 1) In developer.apple.com go to the App Id, and configure the push
#    certificates. Follow Apple's instructions for creating the signing
#    requests and generating the certificates.
#
# 2) Download the certificates and import them into the local keychain.
#
# 3) In Keychain Access, find the certificates, open them and export the
#    _private key_ (not the certificate itself) for each certificate.
#
# 4) Now you should have the downloaded aps.cer and exported aps.p12
#    files. Run this script on those files to produce the aps.pem file.
#
# - Kimmo Kulovesi, 2017-07-21

set -e -o pipefail

p12="$1.p12"
cer="$1.cer"

if [ ! -r "$p12" -o ! -r "$cer" ]; then
    p12="$1"
    cer="$2"
    basename="$(echo "$p12" | sed 's/\.p12$//')"
else
    basename="$1"
fi

if [ ! -r "$p12" -o ! -r "$cer" ]; then
    echo "Usage: $0 file.p12 file.cer" >&2
    exit 1
fi

outfile="$basename.pem"

echo "Converting $cer..."
openssl x509 -in "$cer" -inform der -out "$cer.pem"

echo "Converting $p12..."
openssl pkcs12 -nocerts -in "$p12" -out "$p12.pem"

echo "Decrypting..."
openssl rsa -in "$p12.pem" -out "$p12.raw.pem"

echo "Combining..."
cat "$cer.pem" "$p12.raw.pem" >"$outfile"