gistfile1.rb

class V1::Client::SessionsController < V1::Client::ApplicationController
  skip_before_action :authenticate, only: %i[create]

  def create
    @session = ::Client::Session.new(session_params)
    @session.save
    respond_with @session, location: nil
  end

  private

  def session_params
    params.require(:session).permit(:email, :password)
  end
end

class Client::Session < ActiveModel::Session
  def email=(email)
    @email = email
    @user = Client.find_by(email: email)
  end

  def save
    valid? and user.generate_authentication_token!
  end

  def as_json(*)
    {authentication_token: user.try(:authentication_token)}
  end
end