How is Flask-Login's request_loader related to user_loader?
I need to make this clear.
This is the reason why you shoud use request_loader with flask_login.
There will be a lot of @login_required from flask_login used in your api to guard the request access.
You need to make a request to pass the check of auth.
And there will be a lot of current_user imported from flask_login,
Your app need to use them to let the request act as the identity of the current_user.
There are two ways to achieve the above with flask_login.

Using user_loader makes the request to be OK for @login_required.
It is often used for UI logins from browser.
It will store session cookies to the browser and use them to auth later.
So you need to login only once and the session will keep for a time.

Using request_loader will also be OK with @login_required.
But it is often used with api_key or basic auth.
For example used by other apps to interact with your flask app.
There will be no session cookies,
so you need to provide the auth info every time you send request.


With both user_loader and request_loader,
now you got 2 ways of auth for the same api,
protected by @login_required,
and with current_user usable,
which is really smart.
I apologize in advance for asking a rather cryptic question.  However, I did not understand it despite going through a lot of material. It would be great if you could shed some light on this.
What is the purpose of a request_loader in flask-login?  How does it interact with the user_loader decorator?  
If I am using a token based authentication system (I am planning on sending the token to my angularJS front end, storing the token there and sending that token in the authorization-token header), will I need a request_loader or will a user_loader (where I check the auth header and see if the user exists) suffice?