add user signup flow

app/auth.py

@@ -4,6 +4,7 @@ from argon2 import PasswordHasher
 from functools import wraps
 import secrets
 import time
+import re
 
 ph = PasswordHasher()
 
@@ -44,6 +45,15 @@ def create_session(user_id, temporary=False):
         'expires_at': int(time.time()) + (expires_days * 24 * 60 * 60),
     })
 
+def parse_username(username: str) -> Tuple[str, str]:
+    if len(username) < 3:
+        raise ValueError
+    invalid_regex = r'[^a-zA-Z0-9_-]'
+    return username, re.sub(invalid_regex, '_', username.lower())[:20]
+
+def is_password_valid(password: str) -> bool:
+    return re.match(r'^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[\W_])(?!.*\s).{10,255}$', password) is not None
+
 # annotations
 def login_required(view_func):
     @wraps(view_func)