How to Firebase Auth with Rails?

Question

I have fully integrated Firebase Auth in my Android App, now I want the client to interact with my backend (rails) using a unique Token. my question is this how it's done :

1. User is logged-in, using for example Facebook Auth,
2. Send the Firebase Token to backend and verify it
3. Respond to the client with a unique Token for the upcoming Api requests (get users data, save user data ...)

Thank you

Answer 1

Taking JinLiu's answer forward , once you get the Token in your android code , send it to your backend say : https://www.yourbackend.com?authenticate?token=asdad7687h... Note that the token generated by Firebase is a JWT token , we need to first verify its authenticity and decode it in the backend. For this , you need to add these two gems to your gemfile gem 'jwt' , '1.5.6' gem 'rest-client' , '2.0.1' With that done , you need to add these two (private) function in your controller:

def get_set_user
    begin
        token = params[:token]
        if token.nil?
          @user = nil
          return
        end
        firebase_id = verify_user(token)[0]["user_id"]
        if User.where(:firebase_id => firebase_id).exists?
          @user = User.where(:firebase_id => firebase_id).first
        else
          @user = User.new(:firebase_id => firebase_id)
          @user.save
          @user
        end
    rescue
        @user = nil
    end
end

def verify_user(token)
  certificate_url = "https://www.googleapis.com/robot/v1/metadata/x509/[email protected]"
  myresponse = RestClient.get(certificate_url).body
  certificates  = JSON.parse myresponse.gsub('=>', ':')
  myjson =""
  certificates.each do|key , value|
    begin
      x509 = OpenSSL::X509::Certificate.new(value)
      iss = 'https://securetoken.google.com/<yourdomain>'
      aud = 'yourdomain' # change this 
      myjson = JWT.decode(token, x509.public_key, true, 
      {               algorithm: "RS256", verify_iat: true ,
                      iss: iss , verify_iss: true ,
                      aud: aud , verify_aud: true
      })

      return myjson

    rescue
    end
  end

  return nil     

end

Now you can call get_set_user as before action to see , if the user has valid token . The idea is simple. Check if the token is signed by one of the keys mentioned at https://www.googleapis.com/robot/v1/metadata/x509/[email protected] . If yes , decode the token and get the firebase id .