A Flask extension for handling Cross Origin Resource Sharing (CORS), making cross-origin AJAX possible.

Install the extension with using pip, or easy_install.

$ pip install -U flask-cors

This extension enables CORS support either via a decorator, or a Flask extension. There are three examples shown in the examples directory, showing the major use cases. The suggested configuration is the simple_example.py, or the app_example.py.

In the simplest case, initialize the Flask-Cors extension with default arguments in order to allow CORS on all routes.

app = Flask(__name__)
cors = CORS(app)

@app.route("/")
def helloWorld():
  return "Hello, cross-origin-world!"

Alternatively, a list of resources and associated settings for CORS can be supplied, selectively enables CORS support on a set of paths on your app.

Note: this resources parameter can also be set in your application's config.

app = Flask(__name__)
cors = CORS(app, resources={r"/api/*": {"origins": "*"}})

@app.route("/api/v1/users")
def list_users():
  return "user example"

This extension also exposes a simple decorator to decorate flask routes with. Simply add @cross_origin() below a call to Flask's @app.route(..) incanation to accept the default options and allow CORS on a given route.

@app.route("/")
@cross_origin() # allow all origins all methods.
def helloWorld():
  return "Hello, cross-origin-world!"

Flask-Cors uses standard Python logging, using the logger name 'app.logger_name.cors'. The app's logger name attribute is usually the same as the name of the app. You can read more about logging from Flask's documentation.

import logging
# make your awesome app
logging.basicConfig(level=logging.INFO)

For a full list of options, please see the full documentation

Default : '*'

The origin, or list of origins to allow requests from. The origin(s) may be regular expressions, exact origins, or else an asterisk.

Default : [GET, HEAD, POST, OPTIONS, PUT, PATCH, DELETE]

The method or list of methods which the allowed origins are allowed to access for non-simple requests.

Default : None

The header or list of headers which are safe to expose to the API of a CORS API specification

Default : None

The header or list of header field names which can be used when this resource is accessed by allowed origins.

Default : False

Allows users to make authenticated requests. If true, injects the Access-Control-Allow-Credentials header in responses.

Default : None

The maximum time for which this CORS request maybe cached. This value is set as the Access-Control-Max-Age header.

Default : True

If True, and the origins parameter is *, a wildcard Access-Control-Allow-Origin header is sent, rather than the request's Origin header.

Default : True

If True, CORS headers are sent even if there is no Origin in the request's headers.

Default : True

If True, CORS headers will be returned for OPTIONS requests. For use with cross domain POST requests which preflight OPTIONS requests, you will need to specifically allow the Content-Type header. ** Only applicable for use in the decorator**

Default : True

If True, the header Vary: Origin will be returned as per suggestion by the W3 implementation guidelines. Setting this header when the Access-Control-Allow-Origin is dynamically generated (e.g. when there is more than one allowed origin, and an Origin than '*' is returned) informs CDNs and other caches that the CORS headers are dynamic, and cannot be re-used. If False, the Vary header will never be injected or altered.

Alternatively, you can set all parameters except automatic_options in an app's config object. Setting these at the application level effectively changes the default value for your application, while still allowing you to override it on a per-resource basis, either via the CORS Flask-Extension and regular expressions, or via the @cross_origin() decorator.

The application-wide configuration options are identical to the keyword arguments to cross_origin, creatively prefixed with CORS_

• CORS_ORIGINS
• CORS_METHODS
• CORS_ALLOW_HEADERS
• CORS_EXPOSE_HEADERS
• CORS_ALWAYS_SEND
• CORS_MAX_AGE
• CORS_SEND_WILDCARD
• CORS_ALWAYS_SEND

When using JSON cross origin, browsers will issue a pre-flight OPTIONS request for POST requests. In order for browsers to allow POST requests with a JSON content type, you must allow the Content-Type header. The simplest way to do this is to simply set the CORS_HEADERS configuration value on your application, e.g:

app.config['CORS_HEADERS'] = 'Content-Type'

A simple set of tests is included in test/. To run, install nose, and simply invoke nosetests or python setup.py test to exercise the tests.

Questions, comments or improvements? Please create an issue on Github, tweet at @corydolphin or send me an email.

This Flask extension is based upon the Decorator for the HTTP Access Control written by Armin Ronacher.