Understanding the Magic¶
Flask-Dance might initially seem like magic (“it just works!”), but it’s just code. It’s complicated, but understandable. This page will teach you how Flask-Dance works.
Making the Blueprint¶
The first thing you do with Flask-Dance is make a blueprint. This is
an instance of
OAuth1ConsumerBlueprint
or OAuth2ConsumerBlueprint
,
depending on if you’re using OAuth 1 or OAuth 2. (Most providers use
OAuth 2.)
When you make your blueprint, you can either pass your client ID
and client secret to the blueprint directly, or teach your blueprint
where to find those values on its own using the
from_config
dictionary. Using this
dictionary is usually a good idea, since it allows you to specify
these values in your application configuration instead of in
your code.
After you’ve made the blueprint, you need to register it on your Flask application, just like you would with any other blueprint.
Using the Requests Session¶
The Flask-Dance blueprints have a session
attribute. When you access this attribute, the blueprint
will create and return a requests.Session
object,
properly configured for OAuth authentication. You can use this object
in exactly the same way as you would normally use the Requests
library for making HTTP requests.
The pre-set configurations also allow you to import special objects that refer to these Requests session objects. For example, if you run this code:
from flask_dance.contrib.github import github
You can then call github.get()
just like you do with Requests.
However, this github
object is not actually a Requests session –
it’s something called a LocalProxy
.
This allows you to access the session within the context of an incoming
HTTP request, but it will not allow you access it outside that
context.
Checking Authorization¶
When your application starts up, Flask-Dance will check your token
storage to see if there is an OAuth token already saved
there. If so, the authorized
property on your Requests
Session object will be True
; if not, it will be False
.
You can use this to determine if the user needs to go through the
OAuth dance or not.
Warning
If the OAuth token is expired or invalid, it will not work.
However, this authorized
property can not check this for
you! It only checks if the token exists.
Starting the Dance¶
In order to start the OAuth dance, redirect the user to the
login()
view from your blueprint.
You will need to provide the name of your blueprint when calling
Flask’s url_for()
function. For example, for the
GitHub contrib:
from flask import redirect, url_for
def my_view_func():
# ... implement whatever logic you want here
return redirect(url_for("github.login"))
Finishing the Dance¶
After the user finishes the OAuth dance, they will be redirected
back to the authorized()
view
from your blueprint. This will save the OAuth token to whatever
token storage you are using, and will then redirect the user
to a different page on your website.
By default, the user will be redirected back to the root page (/
).
However, you can set the redirect_url
or redirect_to
arguments
in your blueprint to change this.
If you want a dynamic redirect, where the URL isn’t known until
the user finishes the OAuth dance, hook into the
oauth_authorized
signal and return the redirect from your subscriber function.
For example:
import flask
from flask_dance.consumer import oauth_authorized
@oauth_authorized.connect
def redirect_to_next_url(blueprint, token):
next_url = flask.session["next_url"]
return flask.redirect(next_url)