feat(security): add approved rooms/users/domains as env variables (#277)

* feat(security): add approved rooms/users/domains as env variables
* chore(lint): fix R0902
* chore(lint): fix C0114
* chore(lint): fix C0116
* chore(lint): fix C0413

app/utils/helpers.py

@@ -0,0 +1,16 @@
+"""Standalone helper functions."""
+
+import re
+
+
+def validate_email_syntax(email: str) -> bool:
+    """Validate email syntax.
+
+    Args:
+        email (str): Email address.
+
+    Returns:
+        bool: True if valid, else False.
+    """
+    pattern = r"^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$"
+    return re.match(pattern, email) is not None