How create a omniauth gem for login to gitlab?

Now, I had a PHP+MySQL site. Member 100000+.

I want to write a gem so that these users can log in to my gitlab. but I don't know how to write.

I read all the Gitlab and omniauth articles, that is very simple.

like this: http://docs.gitlab.com/ce/integration/omniauth.html#using-custom-omniauth-providers

sudo service gitlab stop

gem "omniauth-your-auth-provider"

sudo -u git -H bundle install --without development test postgres --path vendor/bundle --no-deployment

sudo service gitlab start

I try to participate in a Facebook to write a gem, and in the IRB test =>true.

But no effect after installation.

Official documents in the more did not explain their own gem, how to modify the configuration file or do not modify.

This is very sad.