Fix 1180: Added information about unique lockout mechanisms (AWS Cognito) to WSTG-ATHN-03. (#1184)

* Added AWS Cognito Testing Info

Contains information on testing for AWS Cognito. First draft. Will come back later for a re-read.

Author: alp1n3-eth

document/4-Web_Application_Security_Testing/04-Authentication_Testing/03-Testing_for_Weak_Lock_Out_Mechanism.md

@@ -38,6 +38,14 @@ To evaluate the account lockout mechanism's ability to mitigate brute force pass
 8. Attempt to log in with the correct password 10 minutes later. The application returns "Your account is locked out.", thereby showing that the lockout mechanism does not automatically unlock after 10 minutes.
 9. Successfully log in with the correct password 15 minutes later, thereby showing that the lockout mechanism automatically unlocks after a 10 to 15 minute period.
 
+#### Unique Lockout Mechanisms
+
+There are more unique implementations of lockout mechanisms in use that are still acceptable. One of which is AWS's [Cognito](https://docs.aws.amazon.com/cognito/latest/developerguide/authentication.html#authentication-flow-lockout-behavior). It uses a simple scaling algorithm that mitigates brute-force attacks while not enabling long-term denial-of-service attacks against the affected user. After 5 failed sign-in attempts with a password, the user is locked out for one second. The lockout duration doubles with each failed attempt, with a maximum of 15 minutes. Sign-in attempts made during the lockout period are exceptions referred to as `Password attempts exceeded`, and in most implementations are not returned to the user who initiated the sign-in. If they aren't shown to the user, a tester may think that no lockout mechanism is being used, as 200 rapid attempts to sign-in would generate a lot of the exceptions, and very few legitimate failed sign-in attempts.
+  
+The math behind the mechanism is: `2^(n-5)`, with `n` being the number of failed sign-in attempts. The resulting number is the amount of seconds that the user is locked out. To reset the lockout count to zero, the user must sign-in successfully or wait the 15 minutes.
+
+To test for this using a fuzzing tool, such as Burp Suite's Intruder, navigate into the "Resource Pool". Then set the maximum concurrent requests to 1 and the delay between requests to 2 seconds. Attempt the invalid authentication 200 times, then attempt to use the valid credentials 3 times directly after the fuzzing tool finishes. Wait 2 minutes and attempt to sign-in. If sign-in is then successful, Cognito may be in use. Further testing can then be performed to validate the use of Cognito by attempting to push the lockout time higher, but it may be easier to validate this information with the client.
+
 A CAPTCHA may hinder brute force attacks, but they can come with their own set of weaknesses, and should not replace a lockout mechanism. A CAPTCHA mechanism may be bypassed if implemented incorrectly. CAPTCHA flaws include:
 
 1. Easily defeated challenge, such as arithmetic or limited question set.