We know that passport is an authentication middleware for Node and it is used to
authenticate requests. Now lets see what is passport.serialize and passport.deserialize. Passport
attaches the profile information to req.user and this occurs as a result of the serializeUser() and
deserializeUser() functions. Passport.serialize and passport.deserialize are used to set id as a cookie in
the user's browser and to get the id from the cookie when it then used to get user info in a callback. The
done() function is an internal function of passport.js and the user id which you provide as the second
arguement of done() function is saved in the session and it is later used to get the whole object using
deserializeUser function. The serializeUser is the one which determines which data in the user object is
to be stored in the session. The first argument of deserializeUser corresponds to the key of user object
this key can be user id, name,email or anything. This key is given as second arguement in done()
function. deserializeUser checks if the key matches with the in memory array or database or any data
resource to get the whole user object.Read more
