abuild-keygen: make size of private key configurable

Previously, a key size of 2048 bits was hardcoded. While this is still
the default, it can now be changed. Additionally, the default key size
might be changed to 4096 in the future.

abuild-keygen.in

@@ -50,7 +50,7 @@ do_keygen() {
 	# generate the private key in a subshell with stricter umask
 	(
 	umask 0007
-	openssl genrsa -out "$privkey" 2048
+	openssl genrsa -out "$privkey" "$numbits"
 	)
 	openssl rsa -in "$privkey" -pubout -out "$pubkey"
 
@@ -92,12 +92,14 @@ usage() {
 		$program $program_version - generate signing keys
 		Usage: $program [-a|--append] [-i|--install] [-n]
 		Options:
-		  -a, --append   Set PACKAGER_PRIVKEY=<generated key> in
-		                 $ABUILD_USERCONF
-		  -i, --install  Install public key into /etc/apk/keys using sudo
-		  -n             Non-interactive. Use defaults
+		  -a, --append         Set PACKAGER_PRIVKEY=<generated key> in
+		                       $ABUILD_USERCONF
+
+		  -i, --install        Install public key into /etc/apk/keys using sudo
+		  -n                   Non-interactive. Use defaults
+		  -b, --numbits [BITS] The size of the private key to generate in bits.
 		  -q, --quiet
-		  -h, --help     Show this help
+		  -h, --help           Show this help
 
 	__EOF__
 }
@@ -105,9 +107,10 @@ usage() {
 append_config=
 install_pubkey=
 non_interactive=
+numbits=2048
 quiet=
 
-args=$(getopt -o ainqh --long append,install,quiet,help -n "$program" -- "$@")
+args=$(getopt -o ab:inqh --long append,numbits:,install,quiet,help -n "$program" -- "$@")
 if [ $? -ne 0 ]; then
 	usage
 	exit 2
@@ -118,6 +121,7 @@ while true; do
 		-a|--append) append_config=1;;
 		-i|--install) install_pubkey=1;;
 		-n) non_interactive=1;;
+		-b|--numbits) numbits="$2"; shift 1;;
 		-q|--quiet) quiet=1;; # suppresses msg
 		-h|--help) usage; exit;;
 		--) shift; break;;