About

OAuth2.0/OpenID authentication with backend in Flask. Also includes:

• Flask-Migration

Starter code forked from https://github.com/udacity/OAuth2.0.

Start Flask app from cmd

Set/register the Flask app (linux):

export FLASK_APP=authApp.py 

then use

flask run

Registering env variables from Flask

Flask allows you to register environment variables that you want to be automatically imported when you run the flask command. To use this option you have to install the python-dotenv package

pip install python-dotenv

Then you can just write the environment variable name and value in a .flaskenv file in the top-level directory of the project:

FLASK_APP=authApp.py

Source: Text taken from The Flask Mega Tutorial Part I

Database/Schema Migration

Prerequisite: FLASK_APP needs to be set as the flask command relies on it.

Create the migration repository

flask db init

This creates a migrations folder in the root directory. The flask db is a sub-command of flask provided by the Flask-Migrate library.

First database migration

flask db migrate -m "restaurant menu table"

The above command does not make any changes to database, it simply generates the migration script. Provide a optional comment using the -m arguement.

A script file is automatically generated in the migrations/versions/ folder, which contains two functions: upgrade() and downgrade()

• upgrade() function applies the migration
• downgrade() function removes it

To upgrade, i.e. apply schema changes and thereby move to a new version:

flask db upgrade

To downgrade, i.e. remove changes and go back to previous version, similarly use:

flask db downgrade

After any modification to the database model/schema, generate a new database migration

flask db migrate -m "user table"

and the upgrade to apply the changes

flask db upgrade

Source: Text taken from The Flask Mega Tutorial Part IV

SQLite, however, throws

ERROR [root] Error: No support for ALTER of constraints in SQLite dialect. 
Please refer to the batch mode feature which allows for SQLite migrations using a copy-and-move strategy.

Thus include the following codes:

convention = {
    "ix": 'ix_%(column_0_label)s',
    "uq": "uq_%(table_name)s_%(column_0_name)s",
    "ck": "ck_%(table_name)s_%(constraint_name)s",
    "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
    "pk": "pk_%(table_name)s"
}

db = SQLAlchemy(app, metadata=MetaData(naming_convention=convention))
if db.engine.url.drivername == 'sqlite':
    migrate = Migrate(app, db, render_as_batch=True)
else:
    migrate = Migrate(app, db)

Populate database

The data is available in lotsofmenus.py file

python lotsofmenus.py

Jinja2/Flask context processors

• Inject new variables automatically into the context of a template using context processors in Flask.
• Context processors run before the template is rendered and have the ability to inject new values into the template context.
• A context processor is a function that returns a dictionary.
• The keys and values of this dictionary are then merged with the template context, for all templates in the app.

Example: Show user in all pages after logging in

@app.context_processor
def inject_user():
    return dict(user_=session['user'] if 'user' in session else {})