https://www.freecodecamp.org/news/how-to-build-a-fullstack-authentication-system-with-react-express-mongodb-heroku-and-netlify/
https://medium.com/@it.ermias.asmare/user-authentication-and-authorization-in-express-and-mongodb-using-jwt-643503a23452
https://medium.com/@anandam00/build-a-secure-authentication-system-with-nodejs-and-mongodb-58accdeb5144
https://medium.com/@diego.coder/autenticaci%C3%B3n-en-node-js-con-json-web-tokens-y-express-ed9d90c5b579