Android Studio can't login to GitHub
Solution 1:
I have faced this problem too. Try using token to login.
Log in to github.com on the browser. Go to Settings -> Developer settings -> Personal access tokens. There you can create a new token and then, go back to Android Studio, select Enter Token at the login prompt.
Solution 2:
I'm working on 4.1.1 Android Studio and it didn't allow me to log in with Login + Password neither.
So I succeeded generating a token from Github (Account -> Settings -> Personal access tokens - > Generate new token), but make sure before generating the token to check the "repo", "gist" and "read:org" options.
Everything's working fine from there.
Have fun coding !