Twitter now allows a two step authentication procedure via third party apps. That means, third party apps such as Google Authenticator, Duo Mobile, Authy etc. could now be used to enter the digit code, used for authentication purposes. Users can choose either the third party apps or that of mobile SMS for this process. Incidentally, the third party apps would keep refreshing the codes on every 30 seconds, making the logging in process more secure.
However, Twitter made it clear that users should have to possess a valid mobile phone number, which is to be associated with their twitter account.