Add exponential backoff of login attempts.

data/model/legacy.py

@@ -1,12 +1,17 @@
 import bcrypt
 import logging
-import datetime
 import dateutil.parser
 import json
 
+from datetime import datetime, timedelta
+
 from data.database import *
 from util.validation import *
 from util.names import format_robot_username
+from util.backoff import exponential_backoff
+
+
+EXPONENTIAL_BACKOFF_SCALE = timedelta(seconds=1)
 
 
 logger = logging.getLogger(__name__)
@@ -68,6 +73,12 @@ class TooManyUsersException(DataModelException):
   pass
 
 
+class TooManyLoginAttemptsException(Exception):
+  def __init__(self, message, retry_after):
+    super(TooManyLoginAttemptsException, self).__init__(message)
+    self.retry_after = retry_after
+
+
 def is_create_user_allowed():
   return True
 
@@ -551,11 +562,30 @@ def verify_user(username_or_email, password):
   except User.DoesNotExist:
     return None
 
+  now = datetime.utcnow()
+
+  if fetched.invalid_login_attempts > 0:
+    can_retry_at = exponential_backoff(fetched.invalid_login_attempts, EXPONENTIAL_BACKOFF_SCALE,
+                                       fetched.last_invalid_login)
+
+    if can_retry_at > now:
+      retry_after = can_retry_at - now
+      raise TooManyLoginAttemptsException('Too many login attempts.', retry_after.total_seconds())
+
   if (fetched.password_hash and 
       bcrypt.hashpw(password, fetched.password_hash) ==
       fetched.password_hash):
+
+    if fetched.invalid_login_attempts > 0:
+      fetched.invalid_login_attempts = 0
+      fetched.save()
+
     return fetched
 
+  fetched.invalid_login_attempts += 1
+  fetched.last_invalid_login = now
+  fetched.save()
+
   # We weren't able to authorize the user
   return None