Greasy Fork

Logging in

1 implement github and bitbicket authorization
2 make it possible to input nickname instead if email into login form (and make email fild not mandatory, if the user havent filled it give him a list of codes for password restoration)
3 implement Secure Remote Protocol to prevent your site from knowing my password

You will take measures 2-3 (or their analogues) if you really care about the users' privacy and security.
Measure 1 is just for convenience : you have already used gh api, why not to add little more gh api usage? And your site mustnt ask information it shouldnt know.

Bue, this was one time nickname. Now this accoint will be sealed with strong password i won't remember.

I disagree. Sites should ask for user emails for verification. Otherwise there is no way to contact users and spam will go up the wall.