How to authenticate a mobile App without username and password?

Question

I\'m building a Webapp that uses OpenId to authenticate users, like Stackoverlfow does. There will be a mobile App too, e.g. Android or iPhone. These Apps have to authenticate o

Answer 1

I'm doing something similar to option (1). Create a unique link (even just include the session id), then send it via SMS. There are plenty of cheap bulk sms providers with simple APIs to do this. When the user clicks on the url in the SMS it will open the mobile web browser and log them in.

After that, if the phone accepts cookies, you can set one. Otherwise the user will always have to come in via that unique link.