As of RS5.1.12a Rockstars Multi-Factor service is available. This will require a time-based security code in addition to your password to login to SA:MP.
IMPORTANT: Please READ everything here and in the service's getting started. I don't want any surprises for people if things aren't done right. This is not a time for TL;DR.
You will need Google Authenticator (or any app which supports TOTP)
Get it from Google Play StoreGet it from App StoreThis service is extremely experimental and may encounter frequent problems which could affect your ability to access the server. We want people to use this to help us find the problems, so we can progress this, but you need to understand and accept the risk.
The service link below will walk you though setting up (note: directions are for Google Auth, if you are using a third-party app please refer to their manual for scanning a barcode). You will need your phone or device you intend on using, it will require an internet connection, and you will need to use it's camera to scan a code.
If you understand how this works and what it is, you can enable it by accessing the link below:
http://samp.argonathrpg.com:3939