Now that we have both the user and the token we can encode a JWT. This is made easy by the
jsonwebtoken library that we will be using.
To create a function that encodes a jwt, the function will need the user and token. Inside the function, definition create a
jwtPayload object that just contains the essential data for encoding. Then, pass the payload to the
sign method and return the signed token.
Finally we store the jwt in the user's localStorage.