The typical way to authenticate user with Twitter is to open the Twitter’s authentication page in a new window/tab. However, this is a bit clunky with mobile browsers.
Is there any nice pattern how to do this as user friendly as possible? Opening the auth page in an iframe is out of question.
Edit: I am building an HTML5 app that should work both on desktop and mobile browsers.
Assuming you’re dealing with a mobile app versus a mobile website, yes, you can do this with xAuth. You will need to get approved by the API team though. Not sure how long that takes.