Fix Docker image to just work without any arguments and drop chown of default data volume

.dockerfiles/entrypoint.sh

@@ -1,10 +1,21 @@
 #!/bin/sh
 
+random_string() {
+  tr -dc 'a-zA-Z0-9' < /dev/urandom | fold -w 64 | head -n 1
+}
+
 [ -n "${PUID}" ] && usermod -u "${PUID}" yarnd
 [ -n "${PGID}" ] && groupmod -g "${PGID}" yarnd
 
-printf "Fixing ownership of default /data volume...\n"
-chown -R yarnd:yarnd /data
+printf "Configuring yarnd..."
+[ -z "${DATA}" ] && DATA="/data"
+[ -z "${STORE}" ] && STORE="bitcask:///data/yarn.db"
+[ -z "${OPEN_REGISTRATIONS}" ] && OPEN_REGISTRATIONS=true
+[ -z "${OPEN_PROFILES}" ] && OPEN_PROFILES=true
+[ -z "${COOKIE_SECRET}" ] && COOKIE_SECRET="$(random_string)"
+[ -z "${MAGICLINK_SECRET}" ] && MAGICLINK_SECRET="$(random_string)"
+[ -z "${API_SIGNING_KEY}" ] && API_SIGNING_KEY="$(random_string)"
+export DATA STORE OPEN_REGISTRATIONS OPEN_PROFILES COOKIE_SECRET MAGICLINK_SECRET API_SIGNING_KEY
 
 printf "Switching UID=%s and GID=%s\n" "${PUID}" "${PGID}"
 exec su-exec yarnd:yarnd "$@"