# Token Storages

A Flask-Dance blueprint has a token storage associated with it, which is an object that knows how to store and retrieve OAuth tokens from some kind of persistent storage. A storage is most often some kind of database, but it doesn’t have to be.

## Flask Session

The default token storage uses the Flask session to store OAuth tokens, which is simple and requires no configuration. However, when the user closes their browser, their OAuth token will be lost, so its not a good choice for production usage.

This is a great option for hobby projects, and for a “proof of concept” to show that an idea is viable.

## SQLAlchemy

SQLAlchemy is the “standard” ORM for Flask applications, and Flask-Dance has great support for it. First, define your database model with a `token` column and a `provider` column. Flask-Dance includes a `OAuthConsumerMixin` class to make this easier:

    from flask_sqlalchemy import SQLAlchemy
    from flask_dance.consumer.storage.sqla import OAuthConsumerMixin

    db = SQLAlchemy()
    class OAuth(OAuthConsumerMixin, db.Model):
        pass

Next, create an instance of the SQLAlchemy storage and assign it to your blueprint:

    from flask_dance.consumer.storage.sqla import SQLAlchemyStorage

    blueprint.storage = SQLAlchemyStorage(OAuth, db.session)

And that’s all you need – if you don’t have user accounts in your application. If you do, it’s slightly more complicated:

    from flask_sqlalchemy import SQLAlchemy
    from flask_login import current_user
    from flask_dance.consumer.storage.sqla import OAuthConsumerMixin, SQLAlchemyStorage

    db = SQLAlchemy()

    class User(db.Model):
        id = db.Column(db.Integer, primary_key=True)
        # ... other columns as needed

    class OAuth(OAuthConsumerMixin, db.Model):
        user_id = db.Column(db.Integer, db.ForeignKey(User.id))
        user = db.relationship(User)

    blueprint.storage = SQLAlchemyStorage(OAuth, db.session, user=current_user)

There are two things to notice here. One, the model that you use for storing OAuth tokens must have a `user` relationship to the user that it is associated with. Two, you must pass a reference to the currently logged-in user (if any) to `SQLAlchemyStorage`. If you’re using Flask-Login, the `current_user` proxy works great, but you could instead pass a function that returns the current user, if you want.

You also probably want to use a caching system for your database, so that it is more performant under heavy load. The SQLAlchemy token storage also integrates with Flask-Caching if you pass an instance of Flask-Caching to the storage, like this:

    from flask import Flask
    from flask_caching import Cache

    app = Flask(__name__)
    cache = Cache(app)

    # setup Flask-Dance with SQLAlchemy models...

    blueprint.storage = SQLAlchemyStorage(OAuth, db.session, cache=cache)

## Custom

Of course, you don’t have to use SQLAlchemy, you’re free to use whatever storage system you want. Writing a custom token storage is easy: just subclass `flask_dance.consumer.storage.BaseStorage` and override the `get()`, `set()`, and `delete()` methods. For example, here’s a storage that uses a file on disk:

    import os
    import os.path
    import json
    from flask_dance.consumer.storage import BaseStorage

    class FileStorage(BaseStorage):
        def __init__(self, filepath):
            super(FileStorage, self).__init__()
            self.filepath = filepath

        def get(self, blueprint):
            if not os.path.exists(self.filepath):
                return None
            with open(self.filepath) as f:
                return json.load(f)

        def set(self, blueprint, token):
            with open(self.filepath, "w") as f:
                json.dump(token, f)

        def delete(self, blueprint):
            os.remove(self.filepath)

Then, just create an instance of your storage and assign it to the `storage` attribute of your blueprint, and Flask-Dance will use it.