Devise authentication via Authentication token header (untested)

application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :authenticate_user_from_token!

  private

  def authenticate_user_from_token!
    authenticate_or_request_with_http_token do |token, options|
      user = User.find_by_authentication_token(token)

      if user && Devise.secure_compare(user.authentication_token, token)
        sign_in user, store: false
      end

      user.present?
    end
  end
end

token_authenticatable.rb

require 'active_support/concern'

module TokenAuthenticatable
  extend ActiveSupport::Concern

  included do
    before_validation :generate_authentication_token, on: :create
    before_save :change_authentication_token, on: :update
  end

  private

  def generate_authentication_token
    self.authentication_token = Devise.token_generator.generate(self.class, :authentication_token)
  end
  
  def change_authentication_token
    generate_authentication_token if encrypted_password_changed?
  end
end

user.rb

class User
  include TokenAuthenticatable
end