Allow disabling brute force prevention

app/models/user.rb

@@ -225,7 +225,9 @@ class User < Principal
     end
     unless prevent_brute_force_attack(result, login).nil?
       user.update_attribute(:last_login_on, Time.now) if user && !user.new_record?
-      return user
+      # don't let brute force prevention allow a user access that was
+      # denied earlier
+      return user if result
     end
     nil
   end
@@ -353,6 +355,7 @@ class User < Principal
   #
   def failed_too_many_recent_login_attempts?
     block_threshold = Setting.brute_force_block_after_failed_logins.to_i
+    return false if block_threshold == 0  # disabled
     return (last_failed_login_within_block_time? and
             self.failed_login_count >= block_threshold)
   end

features/users/brute_force_prevention.feature

@@ -33,3 +33,9 @@ Feature: Prevent brute force attacks
     And I try to log in with user "bob"
     Then I should see "Bob Bobbit"
 
+  Scenario: Brute force prevention is disabled
+    Given users are blocked for 5 minutes after 0 failed login attempts
+    When I try to log in with user "bob" and a wrong password
+    Then I should not see "Bob Bobbit"
+    When I try to log in with user "bob"
+    Then I should see "Bob Bobbit"