doorkeeper.rb

# config/initializers/doorkeeper.rb
Doorkeeper.configure do
  client_credentials :from_obfuscated_params
end

module Doorkeeper
  module OAuth
    class Client
      module Methods
        def from_obfuscated_params(request)
          client_id, client_time, client_digest = request.parameters.values_at(:client_id, :client_time, :client_digest)
          if Time.at(client_time.to_f).between?(15.minutes.ago, 15.minutes.from_now) and app = Doorkeeper::Application.by_uid(client_id)
            calculated_digest = OpenSSL::HMAC::hexdigest(OpenSSL::Digest::SHA1.new, app.secret, client_time)
            if Rack::Utils.secure_compare(client_digest, calculated_digest)
              return [client_id, app.secret]
            end
          end
          [client_id, nil]
        end
      end
    end
  end
end