Allow configuration of user used for task execution

New NEXTCLOUD_EXEC_USER environment variable added which allows control over which
user is used to execute cron tasks inside the Nextcloud container. By default, the
user is `www-data`. If the environment variable is specified but empty, no `--user`
option is provided to `docker exec`.

Dockerfile

@@ -2,6 +2,7 @@ FROM alpine
 
 RUN apk add --no-cache docker bash
 
+ENV NEXTCLOUD_EXEC_USER=www-data
 ENV NEXTCLOUD_CONTAINER_NAME=
 ENV NEXTCLOUD_PROJECT_NAME=
 ENV NEXTCLOUD_CRON_MINUTE_INTERVAL=15

README.md

@@ -59,6 +59,13 @@ entirely.
 * `NEXTCLOUD_CRON_MINUTE_INTERVAL`<br>
   The interval, in minutes, of how often the cron task
   executes. The default is 15 minutes.
+* `NEXTCLOUD_EXEC_USER`<br>
+  The user that should be used to run the cron tasks inside the Nextcloud container. This parameter
+  is specified to the `docker exec` command from this container. By default, the user used is
+  `www-data`, which is also the default user used inside Nextcloud, unless you've overridden it. You
+  may also define this environment variable to be blank (e.g. `NEXTCLOUD_EXEC_USER=`) which results
+  in the tasks being executed using the Nextcloud container's running user. Specifically, the
+  `--user` option will *not* be provided to the `docker exec` command.
 
 # Container Health
 
@@ -67,7 +74,7 @@ is checked every interval of the health check. If any of these checks fail, it i
 container's health status will become *unhealthy*. In this case, you should restart the container.
 
 1. The `crond` process must be running.
-1. The Nextcloud container must be available and running. One important note here: When this
+2. The Nextcloud container must be available and running. One important note here: When this
    container starts up, it immediately searches for the container by name and remembers it by the
    container's ID. If for whatever reason the Nextcloud container changes in such a way that the ID
    is no longer valid, the health check would fail.

scripts/cron-tasks.sh

@@ -5,13 +5,19 @@ echo "-------------------------------------------------------------"
 echo " Executing Cron Tasks: $(date)"
 echo "-------------------------------------------------------------"
 
+# If a user must be specified when executing the task, set up that option here.
+# You may also leave NEXTCLOUD_EXEC_USER blank, in which case it will not be used.
+if [[ -n "$NEXTCLOUD_EXEC_USER" ]]; then
+    exec_user="--user $NEXTCLOUD_EXEC_USER"
+fi
+
 # Loop through all shell scripts and execute the contents of those scripts in the Nextcloud
 # container. It's done this way so that the user may mount more scripts to be executed in addition
 # to the default ones.
 cd /cron-scripts
 for script in *.sh; do
     echo "> Running Script: $script"
-    docker exec -i "$1" bash < $script
+    docker exec $exec_user -i "$1" bash < $script
 done
 
 echo "> Done"