Yubikey two factor auth plugin Version 1 Proof Of Concept

This is a early Proof of Concept for two factor authentication plugin for StatusNet.

Many things are left to do:
GUI for adding Yubikey identifier (first 12 chars of the OTP)
Work across all authentication methods?
Allow users who do not have yubikeys associated to also login (again this is just a POC :)

A few architectural considerations for StatusNet are keeping me from proceeding (also my free time), so I'm sharing what I've done in hopes someone can contribute or offer ideas.

Install:
Put this code in the folder named 'Yubikey' in your StatusNet plugins/ folder.

Generate a new id+key from https://api.yubico.com/get-api-key/

Add this to your config.php:
addPlugin('Yubikey', array('api_key'   => 'xyzexample',
                           'client_id' => '1234'));

Use a SQL query to add your Yubikey identifier (first 12 chars of your OTP) to the user_yubikey table. 
INSERT INTO  `statusnet`.`user_yubikey` (
`yubikey_id` ,
`user_id` ,
`created` ,
`modified`
)
VALUES (
'2134534312',  '1', NOW() , NOW()
);

I've also had to include some extra plugin Events which are in the sn-new-events.patch (off of SN 0.9.2)