Doorkeeper - Assertion Grant Extension

Assertion grant extension for Doorkeeper. Born from: doorkeeper-gem/doorkeeper#249

Installation

Add both gems to your Gemfile.
Add assertion as a grant_flow to your initializer. There are multiple ways to use it:

Reuse devise configuration (returns OmniAuth AuthHash)
Direct Omniauth configuration (returns OmniAuth AuthHash)
Other Alternatives (they are not OmniAuth AuthHash compatible)

Reuse devise configuration

Will automagically load the OmniAuth configs from Devise, and will return a OmniAuth AuthHash. NOTE: server.client will authenticate your client, if you dont need it delete server.client from the if.

Doorkeeper.configure do
  resource_owner_from_assertion do
    if server.client && params[:provider] && params[:assertion]
      auth = Doorkeeper::GrantsAssertion::Devise::OmniAuth.auth_hash(
        provider: params.fetch(:provider),
        assertion: params.fetch(:assertion)
      )
      User.where(email: auth.info.email).first if auth
    end
  end
  # add your supported grant types and other extensions
  grant_flows %w(assertion authorization_code implicit password client_credentials)
end

Direct Omniauth configuration

Reuses OmniAuth strategy implementation, such as facebook or google. This allows you to use the auth_hash, which will return a OmniAuth AuthHash NOTE: server.client will authenticate your client, if you dont need it delete server.client from the if.

Doorkeeper.configure do
  resource_owner_from_assertion do
    if server.client && params[:provider] && params[:assertion]
      case params.fetch(:provider)
      when "google"
        auth = Doorkeeper::GrantsAssertion::OmniAuth.oauth2_wrapper(
          provider: "google",
          strategy_class: OmniAuth::Strategies::GoogleOauth2,
          client_id: ENV["GOOGLE_CLIENT_ID"],
          client_secret: ENV["GOOGLE_CLIENT_SECRET"],
          client_options: { skip_image_info: false },
          assertion: params.fetch(:assertion)
        ).auth_hash rescue nil
        unless auth.nil?
          # your custom finders - just like in devise omniauth
          User.find_by(google_id: auth['id'])
        end
      end
    end
  end
  # add your supported grant types and other extensions
  grant_flows %w(assertion authorization_code implicit password client_credentials)
end

Other Alternatives

Also, lets you define your own way of authenticating resource owners via 3rd Party applications. For example, via Facebook:

Doorkeeper.configure do
  resource_owner_from_assertion do
    facebook = URI.parse('https://graph.facebook.com/me?access_token=' +
    params[:assertion])
    response = Net::HTTP.get_response(facebook)
    user_data = JSON.parse(response.body)
    User.find_by_facebook_id(user_data['id'])
  end

  # add your supported grant types and other extensions
  grant_flows %w(assertion authorization_code implicit password client_credentials)
end

If you want to ensure that resource owners can only receive access tokens scoped to a specific application, you'll need to add that logic in to the definition as well:

Doorkeeper.configure do
  resource_owner_from_assertion do
    Doorkeeper::Application.find_by!(uid: params[:client_id]) #will raise an exception if not found
    facebook = URI.parse('https://graph.facebook.com/me?access_token=' + params[:assertion])
    # ....continue with authentication lookup....
  end
end

More complete examples, also for other providers may be found in the wiki.

IETF standard: http://tools.ietf.org/html/rfc7521

Supported versions

Assertion grant extension for Doorkeeper is tested with Rails 4.2, 5.x and 6.0.

Contributing

After adding the feature and functionality, please run

 bundle exec appraisal install

This will update gems in for travis ci tests.

doorkeeper-grants_assertion

Development