--- a/CHANGES.txt	Sun Apr 28 18:44:05 2019 -0400
+++ b/CHANGES.txt	Sat May 11 17:24:58 2019 -0400
@@ -78,6 +78,10 @@
   nosymessage before it gets sent. See issue:
   https://issues.roundup-tracker.org/issue2551018 for example
   nosyreaction and generated email. (Tom Ekberg (tekberg))
+- issue2550949: Rate limit password guesses/login attempts.  Rate
+  limit mechanism added for web page logins. Default is 3 login
+  attempts/minute for a user. After which one login attempt every 20
+  seconds can be done. (John Rouillard)
 
 Fixed:
 

--- a/roundup/cgi/actions.py	Sun Apr 28 18:44:05 2019 -0400
+++ b/roundup/cgi/actions.py	Sat May 11 17:24:58 2019 -0400
@@ -5,11 +5,15 @@
 from roundup.i18n import _
 from roundup.cgi import exceptions, templating
 from roundup.mailgw import uidFromAddress
+from roundup.rate_limit import Store, RateLimit
 from roundup.exceptions import Reject, RejectRaw
 from roundup.anypy import urllib_
 from roundup.anypy.strings import StringIO
 import roundup.anypy.random_ as random_
 
+import time
+from datetime import timedelta
+
 # Also add action to client.py::Client.actions property
 __all__ = ['Action', 'ShowAction', 'RetireAction', 'RestoreAction', 'SearchAction',
            'EditCSVAction', 'EditItemAction', 'PassResetAction',
@@ -31,6 +35,7 @@
         self.base = client.base
         self.user = client.user
         self.context = templating.context(client)
+        self.loginLimit = RateLimit(self.db.config['WEB_LOGIN_ATTEMPTS_MIN'], timedelta(seconds=60))
 
     def handle(self):
         """Action handler procedure"""
@@ -1226,7 +1231,34 @@
                                            )
 
         try:
-            self.verifyLogin(self.client.user, password)
+            # Implement rate limiting of logins by login name.
+            # Use prefix to prevent key collisions maybe??
+            rlkey="LOGIN-" + self.client.user
+            limit=self.loginLimit
+            s=Store()
+            otk=self.client.db.Otk
+            try:
+                val=otk.getall(rlkey)
+                s.set_tat_as_string(rlkey, val['tat'])
+            except KeyError:
+                # ignore if tat not set, it's 1970-1-1 by default.
+                pass
+            # see if rate limit exceeded and we need to reject the attempt
+            reject=s.update(rlkey, limit)
+
+            # Calculate a timestamp that will make OTK expire the
+            # unused entry 1 hour in the future
+            ts = time.time() - (60 * 60 * 24 * 7) + 3600
+            otk.set(rlkey, tat=s.get_tat_as_string(rlkey),
+                                   __timestamp=ts)
+            otk.commit()
+
+            if reject:
+                # User exceeded limits: find out how long to wait
+                status=s.status(rlkey, limit)
+                raise Reject(_("Logins occurring too fast. Please wait: %d seconds.")%status['Retry-After'])
+            else:
+                self.verifyLogin(self.client.user, password)
         except exceptions.LoginError as err:
             self.client.make_user_anonymous()
             for arg in err.args:

--- a/roundup/configuration.py	Sun Apr 28 18:44:05 2019 -0400
+++ b/roundup/configuration.py	Sat May 11 17:24:58 2019 -0400
@@ -718,6 +718,12 @@
             "variables supplied by your web server (in that order).\n"
             "Set this option to 'no' if you do not wish to use HTTP Basic\n"
             "Authentication in your web interface."),
+        (IntegerNumberOption, 'login_attempts_min', "3",
+            "Limit login attempts per user per minute to this number.\n"
+            "By default the 4th login attempt in a minute will notify\n"
+            "the user that they need to wait 20 seconds before trying to\n"
+            "log in again. This limits password guessing attacks and\n"
+            "shouldn't need to be changed.\n"),
         (SameSiteSettingOption, 'samesite_cookie_setting', "Lax",
             """Set the mode of the SameSite cookie option for
 the session cookie. Choices are 'Lax' or

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/roundup/rate_limit.py	Sat May 11 17:24:58 2019 -0400
@@ -0,0 +1,117 @@
+# Originaly from
+# https://smarketshq.com/implementing-gcra-in-python-5df1f11aaa96?gi=4b9725f99bfa
+# with imports, modifications for python 2, implementation of
+# set/get_tat and marshaling as string, support for testonly
+# and status method.
+
+from datetime import timedelta, datetime
+
+class RateLimit:
+    def __init__(self, count, period):
+        self.count = count
+        self.period = period
+
+    @property
+    def inverse(self):
+        return self.period.total_seconds() / self.count
+
+
+class Store:
+
+    memory = {}
+
+    def get_tat(self, key):
+        # This should return a previous tat for the key or the current time.
+        if key in self.memory:
+            return self.memory[key]
+        else:
+            return datetime.min
+        
+    def set_tat(self, key, tat):
+        self.memory[key] = tat
+
+    def get_tat_as_string(self, key):
+        # get value as string:
+        #  YYYY-MM-DDTHH:MM:SS.mmmmmm
+        # to allow it to be marshalled/unmarshaled
+        if key in self.memory:
+            return self.memory[key].isoformat()
+        else:
+            return datetime.min.isoformat()
+
+        
+    def set_tat_as_string(self, key, tat):
+        # Take value as string and unmarshall:
+        #  YYYY-MM-DDTHH:MM:SS.mmmmmm
+        # to datetime
+        self.memory[key] = datetime.strptime(tat,"%Y-%m-%dT%H:%M:%S.%f")
+
+    def update(self, key, limit, testonly=False):
+        '''Determine if the item assocaited with the key should be
+           rejected given the RateLimit limit.
+        '''
+        now = datetime.utcnow()
+        tat = max(self.get_tat(key), now)
+        separation = (tat - now).total_seconds() 
+        max_interval = limit.period.total_seconds() - limit.inverse
+        if separation > max_interval:
+            reject = True
+        else:
+            reject = False
+            if not testonly:
+                new_tat = max(tat, now) + timedelta(seconds=limit.inverse)
+                self.set_tat(key, new_tat)
+        return reject
+
+    def status(self, key, limit):
+        '''Return status suitable for displaying as headers:
+            X-RateLimit-Limit: calls allowed per period. Period/window
+                is not specified in any api I found.
+            X-RateLimit-Limit-Period: Non standard. Defines period in
+                seconds for RateLimit-Limit.
+            X-RateLimit-Remaining: How many calls are left in this window.
+            X-RateLimit-Reset: window ends in this many seconds (not an
+                 epoch timestamp) and all RateLimit-Limit calls are
+                 available again.
+            Retry-After: if user's request fails, this is the next time there
+                 will be at least 1 available call to be consumed.
+        '''
+
+        ret = {}
+        tat = self.get_tat(key)
+
+        # static defined headers according to limit
+        ret['X-RateLimit-Limit'] = limit.count
+        ret['X-RateLimit-Limit-Period'] = limit.period.total_seconds()
+
+        # status of current limit as of now
+        now = datetime.utcnow()
+
+        ret['X-RateLimit-Remaining'] = min(int(
+            (limit.period - (tat - now)).total_seconds() \
+             /limit.inverse),ret['X-RateLimit-Limit'])
+
+        tat_epochsec = (tat - datetime(1970, 1, 1)).total_seconds()
+        seconds_to_tat = (tat - now).total_seconds()
+        ret['X-RateLimit-Reset'] = max(seconds_to_tat, 0)
+        ret['X-RateLimit-Reset-date'] = "%s"%tat
+        ret['Now'] = (now - datetime(1970,1,1)).total_seconds()
+        ret['Now-date'] = "%s"%now
+
+        if self.update(key, limit, testonly=True):
+            # A new request would be rejected if it was processes.
+            # The user has to wait until an item is dequeued.
+            # One item is dequeued every limit.inverse seconds.
+            ret['Retry-After'] = limit.inverse
+            ret['Retry-After-Timestamp'] = "%s"%(now + timedelta(seconds=limit.inverse))
+        else:
+            # if we are not rejected, the user can post another
+            # attempt immediately.
+            # Do we even need this header if not rejected?
+            # RFC implies this is used with a 503 (or presumably
+            # 429 which may postdate the rfc). So if no error, no header?
+            # ret['Retry-After'] = 0
+            # ret['Retry-After-Timestamp'] = ret['Now-date']
+            pass
+
+        return ret

--- a/test/test_actions.py	Sun Apr 28 18:44:05 2019 -0400
+++ b/test/test_actions.py	Sat May 11 17:24:58 2019 -0400
@@ -7,8 +7,11 @@
 from roundup.cgi.actions import *
 from roundup.cgi.client import add_message
 from roundup.cgi.exceptions import Redirect, Unauthorised, SeriousError, FormError
+from roundup.exceptions import Reject
 
 from roundup.anypy.cmp_ import NoneAndDictComparable
+from time import sleep
+from datetime import datetime
 
 from .mocknull import MockNull
 
@@ -19,6 +22,11 @@
     def setUp(self):
         self.form = FieldStorage(environ={'QUERY_STRING': ''})
         self.client = MockNull()
+        self.client.db.Otk = MockNull()
+        self.client.db.Otk.data = {}
+        self.client.db.Otk.getall = self.data_get
+        self.client.db.Otk.set = self.data_set
+        self.client.db.config = {'WEB_LOGIN_ATTEMPTS_MIN': 20}
         self.client._ok_message = []
         self.client._error_message = []
         self.client.add_error_message = lambda x : add_message(
@@ -31,6 +39,12 @@
             pass
         self.client.instance.interfaces.TemplatingUtils = TemplatingUtils
 
+    def data_get(self, key):
+        return self.client.db.Otk.data[key]
+
+    def data_set(self, key, **value):
+        self.client.db.Otk.data[key] = value
+
 class ShowActionTestCase(ActionTestCase):
     def assertRaisesMessage(self, exception, callable, message, *args,
                             **kwargs):
@@ -357,6 +371,30 @@
         self.assertLoginRaisesRedirect("http://whoami.com/path/issue255?%40error_message=Invalid+login",
                                  'foo', 'wrong', "http://whoami.com/path/issue255")
 
+    def testLoginRateLimit(self):
+        ''' Set number of logins in setup to 20 per minute. Three second
+            delay between login attempts doesn't trip rate limit.
+            Default limit is 3/min, but that means we sleep for 20
+            seconds so I override the default limit to speed this up.
+        '''
+        # Do the first login setting an invalid login name
+        self.assertLoginLeavesMessages(['Invalid login'], 'nouser')
+        # use up the rest of the 20 login attempts
+        for i in range(19):
+            self.client._error_message = []
+            self.assertLoginLeavesMessages(['Invalid login'])
+
+        self.assertRaisesMessage(Reject, LoginAction(self.client).handle,
+               'Logins occurring too fast. Please wait: 3 seconds.')
+
+        sleep(3) # sleep as requested so we can do another login
+        self.client._error_message = []
+        self.assertLoginLeavesMessages(['Invalid login']) # this is expected
+        
+        # and make sure we need to wait another three seconds
+        self.assertRaisesMessage(Reject, LoginAction(self.client).handle,
+               'Logins occurring too fast. Please wait: 3 seconds.')
+
 class EditItemActionTestCase(ActionTestCase):
     def setUp(self):
         ActionTestCase.setUp(self)