From 87e6ced8ecd0ba54af1f67319fccf96c13ba6261 Mon Sep 17 00:00:00 2001
From: Mitsuo Tokumori <rtokumori@pucp.edu.pe>
Date: Fri, 27 Oct 2023 19:05:20 -0500
Subject: Add authentication logic

---
 README.md          |  10 +++++-
 flaskr/__init__.py |   2 +-
 flaskr/auth.py     | 102 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 112 insertions(+), 2 deletions(-)
 create mode 100644 flaskr/auth.py

diff --git a/README.md b/README.md
index 17876c2..6433ba2 100644
--- a/README.md
+++ b/README.md
@@ -24,4 +24,12 @@ Concepts:
 * flask.open_resource:  From app package path
 * request: HTML request???
 * Factory function > registered functions and blueprints.
-* Blueprint > views & other code
\ No newline at end of file
+* Blueprint: groups views & other code
+* View: function that returns HTML
+* flask.session: dict that stores data across requests (cookies) (securely
+  signed with SECRET_KEY)
+* *endpoint*: name associated with a view, `<blueprint_name>.<view_function_name>`
+
+Gotchas:
+
+* Remember to call db.commit() after modifying DB (DML).
\ No newline at end of file
diff --git a/flaskr/__init__.py b/flaskr/__init__.py
index 19d5a1e..dffc858 100644
--- a/flaskr/__init__.py
+++ b/flaskr/__init__.py
@@ -25,7 +25,7 @@ def create_app(test_config=None):
 
     # Routes
     @app.route('/')
-    def hello():
+    def index():
         return 'Hello, World!'
 
     # Register functions and blueprints
diff --git a/flaskr/auth.py b/flaskr/auth.py
new file mode 100644
index 0000000..3689eba
--- /dev/null
+++ b/flaskr/auth.py
@@ -0,0 +1,102 @@
+"""Authentication blueprint"""
+
+import functools
+
+from flask import (
+    Blueprint, flash, g, redirect, render_template, request, session, url_for
+)
+from werkzeug.security import check_password_hash, generate_password_hash
+from flaskr.db import get_db
+
+bp = Blueprint('auth', __name__, url_prefix='/auth')
+
+@bp.route('/register', methods=('GET', 'POST'))
+def register():
+    if request.method == 'POST':
+        # Form validation
+        username = request.form['username']
+        password = request.form['password']
+        db = get_db()
+        error = None
+
+        if not username:
+            error = 'Username is required.'
+        elif not password:
+            error = 'Password is required.'
+
+        if error is None:
+            try:
+                # NOTE: don't use f-string here.  Use `?` placeholders so that
+                # database library can escape the fields 
+                # (otherwise SQL injection vulnerability)
+                db.execute(
+                    "INSERT INTO user (username, password) VALUES (?, ?)",
+                    (username, generate_password_hash(password)),
+                )
+                db.commit()
+            except db.IntegrityError:
+                error = f"User {username} is already registered."
+            else:
+                return redirect(url_for("auth.login"))
+
+        flash(error)
+
+    return render_template('auth/register.html')
+
+
+@bp.route('/login', methods=('GET', 'POST'))
+def login():
+    if request.method == 'POST':
+        username = request.form['username']
+        password = request.form['password']
+        db = get_db()
+        error = None
+        user = db.execute(
+            'SELECT * FROM user WHERE username = ?', (username,)
+        ).fetchone()
+
+        if user is None:
+            error = 'Incorrect username.'
+        elif not check_password_hash(user['password'], password):
+            error = 'Incorrect password.'
+
+        if error is None:
+            session.clear()
+            session['user_id'] = user['id']
+            return redirect(url_for('index'))
+
+        flash(error)
+
+    return render_template('auth/login.html')
+
+
+# runs before the view function, no matter what URL is requested
+@bp.before_app_request
+def load_logged_in_user():
+    user_id = session.get('user_id')
+
+    if user_id is None:
+        g.user = None
+    else:
+        g.user = get_db().execute(
+            'SELECT * FROM user WHERE id = ?', (user_id,)
+        ).fetchone()
+
+
+@bp.route('/logout')
+def logout():
+    session.clear()
+    return redirect(url_for('index'))
+
+
+# Define decorator to require authentication in other views
+def login_required(view):
+    """view is a function that returns HTML (and is part of a blueprint)"""
+    @functools.wraps(view)
+    def wrapped_view(**kwargs):
+        if g.user is None:
+            return redirect(url_for('auth.login'))
+
+        return view(**kwargs)
+
+    return wrapped_view
\ No newline at end of file
-- 
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