Yeah, that was an error in the documentation;

all you need is:

$consumerKey = "Your twitter app consumer key"; //twitter app consumer key.
$consumerSecret = "Your twitter app consumer secret"; //twitter app consumer secret.
$oauthToken = "Your my access oauth token"; //twitter app "my access" token
$oauthTokenSecret = "Your my access oauth token secret"; //twitter app "my access" token secret.
for twitter to work.

Just ignore the username and password stuff.