Use Environment Variables (#123)

Uses environment variables instead of hard coding the "deck" user/group.
This adds support for systems other than the steam deck that are using the DeckUI.

* Use Environment Variables

* Use method to get USER from a systemd root process

* Fix imports. Add get_user and get_user_group methods in helpers.py. Removed duplicated code

* Add separate setters/getters for user vars. Ensure sleep prevents race condition of user setter in while loop

backend/helpers.py

@@ -1,11 +1,15 @@
-from aiohttp.web import middleware, Response
-import ssl
 import certifi
+import ssl
 import uuid
 
-ssl_ctx = ssl.create_default_context(cafile=certifi.where())
+from subprocess import check_output
+from time import sleep
 
+# global vars
 csrf_token = str(uuid.uuid4())
+ssl_ctx = ssl.create_default_context(cafile=certifi.where())
+user = None
+group = None
 
 def get_ssl_context():
     return ssl_ctx
@@ -17,4 +21,41 @@ def get_csrf_token():
 async def csrf_middleware(request, handler):
     if str(request.method) == "OPTIONS" or request.headers.get('Authentication') == csrf_token or str(request.rel_url) == "/auth/token" or str(request.rel_url).startswith("/plugins/load_main/") or str(request.rel_url).startswith("/static/") or str(request.rel_url).startswith("/legacy/") or str(request.rel_url).startswith("/steam_resource/"):
         return await handler(request)
-    return Response(text='Forbidden', status='403')
+    return Response(text='Forbidden', status='403')
+
+# Get the user by checking for the first logged in user. As this is run
+# by systemd at startup the process is likely to start before the user
+# logs in, so we will wait here until they are available. Note that
+# other methods such as getenv wont work as there was no $SUDO_USER to
+# start the systemd service.
+def set_user():
+    global user
+    cmd = "who | awk '{print $1}' | sort | head -1"
+    while user == None:
+        name = check_output(cmd, shell=True).decode().strip()
+        if name not in [None, '']:
+            user = name
+        sleep(0.1)
+
+# Get the global user. get_user must be called first.
+def get_user() -> str:
+    global user
+    if user == None:
+        raise ValueError("helpers.get_user method called before user variable was set. Run helpers.set_user first.")
+    return user
+
+# Set the global user group. get_user must be called first
+def set_user_group() -> str:
+    global group
+    global user
+    if user == None:
+        raise ValueError("helpers.set_user_dir method called before user variable was set. Run helpers.set_user first.")
+    if group == None:
+        group = check_output(["id", "-g", "-n", user]).decode().strip()
+
+# Get the group of the global user. set_user_group must be called first.
+def get_user_group() -> str:
+    global group
+    if group == None:
+        raise ValueError("helpers.get_user_group method called before group variable was set. Run helpers.set_user_group first.")
+    return group