This is the OAuth2 strategy for authenticating to your GitLab service.

Gitlab 7.7.0+

Add this line to your application's Gemfile:

gem 'omniauth-gitlab'

And then execute:

$ bundle

Or install it yourself as:

$ gem install omniauth-gitlab

use OmniAuth::Builder do
  provider :gitlab, ENV['GITLAB_KEY'], ENV['GITLAB_SECRET']
end

use OmniAuth::Builder do
  provider :gitlab, ENV['GITLAB_KEY'], ENV['GITLAB_SECRET'],
    {
       client_options: {
         site: 'https://gitlab.YOURDOMAIN.com'
       }
    }
end

By default, the api scope is requested and must be allowed in GitLab's application configuration. To use different scopes:

use OmniAuth::Builder do
  provider :gitlab, ENV['GITLAB_KEY'], ENV['GITLAB_SECRET'], scope: 'read_user openid'
end

Requesting a scope that is not configured will result the error "The requested scope is invalid, unknown, or malformed.".

API V3 will be unsupported from GitLab 9.5 and will be removed in GitLab 9.5 or later.

https://gitlab.com/help/api/v3_to_v4.md

If you use GitLab 9.0 and below you could configure V3 API:

use OmniAuth::Builder do
  provider :gitlab, ENV['GITLAB_KEY'], ENV['GITLAB_SECRET'],
    {
       client_options: {
         site: 'https://gitlab.YOURDOMAIN.com/api/v3'
       }
    }
end

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request