Bug 18314: Account lockout

Bug 18314: Account lockout

To prevent brute force attacks on Koha accounts, staff and opac, we need to
implement an account lockout process to Koha.

After a number of failed login attempts a users account would become locked.
The user would then need to use the reset password functionality to send a reset
token to their email account. After a successful password reset the lockout flag
would be removed.

The number of failed login attempts before lockout is configurable using a new
system preference 'FailedLoginAttempts'.

How does it work?
When a patron enter an invalid password, the borrowers.login_attempts value
for this patron is incremented. When this value reach the value of the
pref FailedLoginAttempts, the password comparison is not done and the
authentication is rejected.
This login_attempts field is reset when a patron correctly logs in. When
the account is locked the patron has to reset his/her password using
the OpacResetPassword feature or ask a staff member to generate a new
password.
If the pref is not set (0, or '') the feature is considered as disabled,
but the failed login attempts are stored anyway.

Test plan:
0/ Apply patch and execute the update DB entry
1/ Switch on the feature by setting FailedLoginAttempts to 3
2/ Use an invalid password to login at the staff or OPAC interface
3/ After the third consecutive failures, you will be asked to reset your
password if OpacResetPassword is set, or contact a staff member
4/ Switch on OpacResetPassword and reset your password
5/ Confirm that you are able to login
6/ Play with the different combinations

QA details: The trick happens in C4::Auth::checkpw, to make things clear
I had to create a return value (note the awesome name: @return) and
replace the 3 successives if statements with elsif. Indeed if one of
the condition is reached, it will return inside the given block.

Signed-off-by: Jonathan Field <jonathan.field@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>