How to add a login endpoint to the REST API

Now that we've done registration, we can do log in! It's very similar.

Let's import flask_jwt_extended.create_access_token so that when we receive a valid username and password from the client, we can create a JWT and send it back:

resources/user.py

from flask.views import MethodView
from flask_smorest import Blueprint, abort
+from flask_jwt_extended import create_access_token
from passlib.hash import pbkdf2_sha256

Then let's create our UserLogin resource.

resources/user.py

@blp.route("/login")
class UserLogin(MethodView):
    @blp.arguments(UserSchema)
    def post(self, user_data):
        user = UserModel.query.filter(
            UserModel.username == user_data["username"]
        ).first()

        if user and pbkdf2_sha256.verify(user_data["password"], user.password):
            access_token = create_access_token(identity=user.id)
            return {"access_token": access_token}, 200

        abort(401, message="Invalid credentials.")

Here you can see the when we call create_access_token(identity=user.id) we pass in the user's id. This is what gets stored (among other things) inside the JWT, so when the client sends the JWT back on every request, we can tell who the JWT belongs to.