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How to add logout to the REST API

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To log an user out we must revoke their JWT. That way, if they send us the same JWT again, we can check whether it's been revoked or not. If it has, then we won't authorize them.

To do this, we need a central store of revoked JWTs that we keep around at least until the revoked JWT has expired.

Let's create our central revoked JWT storage in a file called blocklist.py. You could store this in the database instead, if you prefer. I'll leave that as an exercise for you.

blocklist.py
"""
blocklist.py

This file just contains the blocklist of the JWT tokens. It will be imported by
app and the logout resource so that tokens can be added to the blocklist when the
user logs out.
"""

BLOCKLIST = set()

Flask-JWT-Extended blocklist configuration for user logout​

Now, in app.py, let's add some more Flask-JWT-Extended configuration to do two things:

  • Check whether any JWT received is in the blocklist.
  • If they are, return an error message to that effect.
app.py
from blocklist import BLOCKLIST

...

@jwt.token_in_blocklist_loader
def check_if_token_in_blocklist(jwt_header, jwt_payload):
    return jwt_payload["jti"] in BLOCKLIST


@jwt.revoked_token_loader
def revoked_token_callback(jwt_header, jwt_payload):
    return (
        jsonify(
            {"description": "The token has been revoked.", "error": "token_revoked"}
        ),
        401,
    )

How to perform logout (i.e. add JWTs to the blocklist)​

Finally we need a resource in resources/user.py to actually add the user's JWT to the blocklist when they log out.

resources/user.py
from flask.views import MethodView
from flask_smorest import Blueprint, abort
from flask_jwt_extended import (
    create_access_token,
    get_jwt,
    jwt_required,
)
from passlib.hash import pbkdf2_sha256

from db import db
from models import UserModel
from schemas import UserSchema
from blocklist import BLOCKLIST


blp = Blueprint("Users", "users", description="Operations on users")

@blp.route("/logout")
class UserLogout(MethodView):
    @jwt_required()
    def post(self):
        jti = get_jwt()["jti"]
        BLOCKLIST.add(jti)
        return {"message": "Successfully logged out"}, 200


# Other User routes here