Flask-CORS

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

Installation

Install the extension with using pip, or easy_install.

$ pip install -U flask-cors

Usage

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.

Simple Usage

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!"

Resource specific CORS

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"

Route specific CORS via decorator

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!"

Options

origins

Default : '*'

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

methods

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

The method or list of methods which the allowed origins are allowed to access.

headers

Default : None

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

expose_headers

Default : None

The header or list of headers which are are safe to expose to browsers.

supports_credentials

Default : False

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

max_age

Default : None

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

send_wildcard

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.

always_send

Default : True

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

automatic_options

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**

vary_header

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.

Application-wide options

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_HEADERS
• CORS_EXPOSE_HEADERS
• CORS_ALWAYS_SEND
• CORS_MAX_AGE
• CORS_SEND_WILDCARD
• CORS_ALWAYS_SEND

Using JSON with CORS

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'

Documentation

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

Tests

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.

Contributing

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

Credits

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