Task 6: implement the API for user login

[yalgorithm777]

• Path:
  • /user/
• Available methods:
  • POST
• Required fields (front-end provides to the back-end):
  • “client_id”: the client ID obtained from Google Analytics, or a random string created by the front-end
• Returned fields (back-end returns to the front-end):
  • "user_token": user token for the front-end client, issued by the back-end