Site Login Behavior For SharePoint Foundation 2013 Users With Expired Passwords?

Question

What are the most user-friendly ways of getting external users with expired AD passwords back into the SharePoint site with a new working password?
We already send automated email notifications to users reminding them to change their soon-to-expire passwords.  However, sometimes they miss seeing the email notifications before the password expires (such as after returning from vacation or just carelessness
and lack of attention to email messages) or they see the warning messages and forget to act on it.
When this happens and they try to log into the SharePoint site from the Internet, their login fails without telling the user the reason they can't log in is because their password expired.  So, they end up confused and call the help desk to get their
password reset.
Is there a way to set up SharePoint Foundation 2013 login in a similar way to the OWA login so that, when a user with a correct but expired password tries to log in, it gives them a prompt to set a new password right there rather than just an error indicating
their login failed for unknown reasons or password is "incorrect?"

Answer 1

It could be done. You get a different event log entry for an expired login attempt than for a wrong password, 4625 events denote a login failure and an error ID of 23 denotes a logon failure.
A naff, but simple, approach would be to create a tool that checks your server logon event log for 4625 entries and then emails that user, or the help desk, or security, that they're trying to get onto your system with expired credentials.
For a more polished experience you've got a lot more work and bluntly it's going to be impractical for you. You'd have to re-write sections of the SharePoint authentication process or intercept the process, both are risky and not a good idea to try.
There's a really interesting paper here that might be of interest, it won't help you in your current situation but it might shed more light on the overall authentication/authorisation process.
http://www.sans.org/reading-room/whitepapers/forensics/windows-logon-forensics-34132