Doorkeeper - Assertion Grant Extension

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

Installation

1. Add both gems to your Gemfile.
2. Add assertion as a grant_flow to your initializer.

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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....

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

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