The phrase 'able to login successfully' is grammatically correct and can be used in written English. You can use it when you are referring to someone's ability to log into a system or website successfully. For example, "After a few tries, he was finally able to login successfully.".
[Users] used to be able to login to Facebook and Twitter using VPN.
You will also be able to login with your Twitter or Facebook account.
Apparently, some people are able to login, but when they try do anything, nothing works.
When he entered it, he was able to login and see that her phone number and regular email account were linked to the faux account.
After returning the informed consent form, the patient obtains a personalized code by e-mail and is able to login to the web-questionnaires.
You will be able to login as long as you want.
Don't forget to set a password, or you might not be able to login as this user.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union