refactor: better email validation

1 files changed, 12 insertions, 19 deletions

diff --git a/auth_backend.py b/auth_backend.py
index 00a5dbc..817f8d4 100644
--- a/auth_backend.py
+++ b/auth_backend.py
@@ -9,13 +9,13 @@ import uuid
 from pathlib import Path
 from typing import Callable, Optional, Protocol
 
+from email_validator import EmailNotValidError, validate_email
+
 
 # fixed challenge text used for passphrase verification.
 # we store encrypted challenge output instead of storing passwords.
 AUTH_CHALLENGE = "SHIM_AUTH_VALID"
 HANDLE_RE = re.compile(r"^[a-z0-9_.-]{2,64}$")
-EMAIL_LOCAL_RE = re.compile(r"^[a-z0-9!#$%&'*+/=?^_`{|}~.-]{1,64}$")
-EMAIL_DOMAIN_LABEL_RE = re.compile(r"^[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?$")
 UUID_RE = re.compile(
     r"^[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$"
 )
@@ -54,25 +54,18 @@ def normalize_uuid(value: str) -> Optional[str]:
 def is_valid_email_username(value: str) -> bool:
     if len(value) > 254:
         return False
-    if "@" not in value or value.count("@") != 1:
-        return False
-
-    local_part, domain = value.split("@", 1)
-    if not local_part or not domain:
-        return False
-    if local_part.startswith(".") or local_part.endswith(".") or ".." in local_part:
-        return False
-    if not EMAIL_LOCAL_RE.fullmatch(local_part):
+    try:
+        validated = validate_email(
+            value,
+            check_deliverability=False,
+            allow_smtputf8=False,
+            allow_display_name=False,
+        )
+    except EmailNotValidError:
         return False
 
-    labels = domain.split(".")
-    if len(labels) < 2:
-        return False
-    if any(not label for label in labels):
-        return False
-    if len(labels[-1]) < 2:
-        return False
-    return all(EMAIL_DOMAIN_LABEL_RE.fullmatch(label) for label in labels)
+    # keep stored usernames predictable - only accept already normalized forms.
+    return validated.normalized == value
 
 
 def looks_like_python_script(path: Path) -> bool: