How do you use a license key/server to authenticate a Flask app?

I have a service that generates a license key, and that provides an API to verify the key is valid, e.g. curl api-url -d "license_key=xxxx" -X post returns json that says if the key is valid or not.

I want to use this for authentication in a flask app, where the user enters their key to login, and the app does the check above to authenticate if they have access. The users don't need a username, the license key is unique to them, and should be all that is needed.

I have not found anything that (at least to my understanding) suggests how to go about this in either https://flask-security-too.readthedocs.io/en/stable/ or https://flask-login.readthedocs.io/en/latest/.

I guess it isn't crucial it is done in Flask, if there is another way to do this with a regular web server.

Does this kind of authentication have a name? I feel like I am not looking for the right information so far.

Solution

This can be done using sessions in Flask. You can make the POST request with the requests module.

from flask import Flask, redirect, url_for, render_template, flash, session
from flask_wtf import FlaskForm
from wtforms import StringField, SubmitField
from wtforms.validators import DataRequired
import requests

app = Flask(__name__)
app.config["SECRET_KEY"] = "secret-key-goes-here"  

class LoginForm(FlaskForm):
    license_key = StringField("License key", validators = [DataRequired()])
    submit = SubmitField("Submit")

@app.route("/login", methods=["GET", "POST"])
def login():
    if session.get("authenticated"):
        return redirect(url_for("index"))
    form = LoginForm()
    if form.validate_on_submit():
        req = requests.post("api-url", {"license_key": form.license_key.data})
        if not req.json()["valid"]:
            flash("Invalid username or password")
            return redirect(url_for("login"))
        session["authenticated"] = True
        return redirect(url_for("index"))
    return render_template("login.html", title="Sign In", form=form)

This assumes the JSON response is of the form {"valid": true/false}.