Provided by: python3-flask-cors_4.0.0-1_all 
NAME
flask-cors - Flask-Cors Documentation
A Flask extension for handling Cross Origin Resource Sharing (CORS), making cross-origin
AJAX possible.
This package has a simple philosophy: when you want to enable CORS, you wish to enable it
for all use cases on a domain. This means no mucking around with different allowed
headers, methods, etc.
By default, submission of cookies across domains is disabled due to the security
implications. Please see the documentation for how to enable credential'ed requests, and
please make sure you add some sort of CSRF protection before doing so!
INSTALLATION
Install the extension with using pip, or easy_install.
$ pip install -U flask-cors
USAGE
This package exposes a Flask extension which by default enables CORS support on all
routes, for all origins and methods. It allows parameterization of all CORS headers on a
per-resource level. The package also contains a decorator, for those who prefer this
approach.
Simple Usage
In the simplest case, initialize the Flask-Cors extension with default arguments in order
to allow CORS for all domains on all routes. See the full list of options in the
documentation.
from flask import Flask
from flask_cors import CORS
app = Flask(__name__)
CORS(app)
@app.route("/")
def helloWorld():
return "Hello, cross-origin-world!"
Resource specific CORS
Alternatively, you can specify CORS options on a resource and origin level of granularity
by passing a dictionary as the resources option, mapping paths to a set of options. See
the full list of options in the documentation.
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(..) to allow CORS on a given route.
See the full list of options in the decorator documentation.
@app.route("/")
@cross_origin()
def helloWorld():
return "Hello, cross-origin-world!"
DOCUMENTATION
For a full list of options, please see the full documentation
TROUBLESHOOTING
If things aren't working as you expect, enable logging to help understand what is going on
under the hood, and why.
logging.getLogger('flask_cors').level = logging.DEBUG
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.
If nosetests does not work for you, due to it no longer working with newer python
versions. You can use pytest to run the tests instead.
CONTRIBUTING
Questions, comments or improvements? Please create an issue on Github, tweet at
@corydolphin or send me an email. I do my best to include every contribution proposed in
any way that I can.
CREDITS
This Flask extension is based upon the Decorator for the HTTP Access Control written by
Armin Ronacher.
This Flask extension is based upon the Decorator for the HTTP Access Control written by
Armin Ronacher.
Configuration
Flask-CORS can be configured at four different locations. Configuration values are
determined in the following order:
1. Resource level settings (e.g when passed as a dictionary)
2. Keyword argument settings
3. App level configuration settings (e.g. CORS_*)
4. Default settings
See below for more information.
Configuration options
Configuration options are consistently named across the various locations where they can
be set. A configuration option called example can be set with the resource dictionary key
example, as the keyword argument example or as the Flask app configuration key
CORS_EXAMPLE.
The configuration options recognised by Flask-CORS are:
CORS_ALLOW_HEADERS (List or str)
Headers to accept from the client. Headers in the Access-Control-Request-Headers
request header (usually part of the preflight OPTIONS request) matching headers in
this list will be included in the Access-Control-Allow-Headers response header.
CORS_ALWAYS_SEND (bool)
Usually, if a request doesn't include an Origin header, the client did not request
CORS. This means we can ignore this request.
However, if this is true, a most-likely-to-be-correct value is still set.
CORS_AUTOMATIC_OPTIONS (bool)
Only applies to the flask_cors.cross_origin() decorator. If True, Flask-CORS will
override Flask’s default OPTIONS handling to return CORS headers for OPTIONS
requests.
CORS_EXPOSE_HEADERS (List or str)
The CORS spec requires the server to give explicit permissions for the client to
read headers in CORS responses (via the Access-Control-Expose-Headers header).
This specifies the headers to include in this header.
CORS_INTERCEPT_EXCEPTIONS (bool)
Whether to deal with Flask exception handlers or leave them alone (with respect to
CORS headers).
CORS_MAX_AGE (timedelta, int or str)
The maximum time for which this CORS request may be cached. This value is set as
the Access-Control-Max-Age header.
CORS_METHODS (List or str)
The method(s) which the allowed origins are allowed to access. These are included
in the Access-Control-Allow-Methods response headers to the preflight OPTIONS
requests.
CORS_ORIGINS (List, str or re.Pattern)
The origin(s) to allow requests from. An origin configured here that matches the
value of the Origin header in a preflight OPTIONS request is returned as the value
of the Access-Control-Allow-Origin response header.
CORS_RESOURCES (Dict, List or str)
The series of regular expression and (optionally) associated CORS options to be
applied to the given resource path.
If the value is a dictionary, it's keys must be regular expressions matching
resources, and the values must be another dictionary of configuration options, as
described in this section.
If the argument is a list, it is expected to be a list of regular expressions
matching resources for which the app-wide configured options are applied.
If the argument is a string, it is expected to be a regular expression matching
resources for which the app-wide configured options are applied.
CORS_SEND_WILDCARD (bool)
If CORS_ORIGINS is "*" and this is true, then the Access-Control-Allow-Origin
response header's value with be "*" as well, instead of the value of the Origin
request header.
CORS_SUPPORTS_CREDENTIALS (bool)
Allows users to make authenticated requests. If true, injects the
Access-Control-Allow-Credentials header in responses. This allows cookies and
credentials to be submitted across domains.
note This option cannot be used in conjunction with a "*" origin
CORS_VARY_HEADER: (bool)
Enables or disables the injection of the Vary response header is set to Origin.
This informs clients that our CORS headers are dynamic and cannot be cached.
Default values
• CORS_ALLOW_HEADERS: "*"
• CORS_ALWAYS_SEND: True
• CORS_AUTOMATIC_OPTIONS: True
• CORS_EXPOSE_HEADERS: None
• CORS_INTERCEPT_EXCEPTIONS: True
• CORS_MAX_AGE: None
• CORS_METHODS: ["GET", "HEAD", "POST", "OPTIONS", "PUT", "PATCH", "DELETE"]
• CORS_ORIGINS: "*"
• CORS_RESOURCES: r"/*"
• CORS_SEND_WILDCARD: False
• CORS_SUPPORTS_CREDENTIALS: False
• CORS_VARY_HEADER: True
Locations
Resource level settings
You can specify CORS options on a resource level of granularity by passing a dictionary as
the resources keyword argument when instantiating the flask_cors.CORS object (or when
calling init_app on it), mapping paths to a set of options.
Keyword argument settings
For options matching all resources, it's also possible to simply set the configuration
options using keyword arguments when instantiating the flask_cors.CORS object (or when
calling init_app on it).
App level configuration settings
It's good practice to keep your application configuration settings in one place. This is
also possible with Flask-CORS using the same configuration options in the Flask
application's config object.
Default settings
Finally, every setting has a default value as well.
API Docs
This package exposes a Flask extension which by default enables CORS support on all
routes, for all origins and methods. It allows parameterization of all CORS headers on a
per-resource level. The package also contains a decorator, for those who prefer this
approach.
Extension
This is the suggested approach to enabling CORS. The default configuration will work well
for most use cases.
class flask_cors.CORS(app=None, **kwargs)
Initializes Cross Origin Resource sharing for the application. The arguments are
identical to cross_origin(), with the addition of a resources parameter. The
resources parameter defines a series of regular expressions for resource paths to
match and optionally, the associated options to be applied to the particular
resource. These options are identical to the arguments to cross_origin().
The settings for CORS are determined in the following order
1. Resource level settings (e.g when passed as a dictionary)
2. Keyword argument settings
3. App level configuration settings (e.g. CORS_*)
4. Default settings
Note: as it is possible for multiple regular expressions to match a resource path,
the regular expressions are first sorted by length, from longest to shortest, in
order to attempt to match the most specific regular expression. This allows the
definition of a number of specific resource options, with a wildcard fallback for
all other resources.
Parameters
• resources (dict, iterable or string) --
The series of regular expression and (optionally) associated CORS options
to be applied to the given resource path.
If the argument is a dictionary, it's keys must be regular expressions,
and the values must be a dictionary of kwargs, identical to the kwargs of
this function.
If the argument is a list, it is expected to be a list of regular
expressions, for which the app-wide configured options are applied.
If the argument is a string, it is expected to be a regular expression for
which the app-wide configured options are applied.
Default : Match all and apply app-level configuration
• origins (list, string or regex) --
The origin, or list of origins to allow requests from. The origin(s) may
be regular expressions, case-sensitive strings, or else an asterisk.
note origins must include the schema and the port (if not port 80),
e.g., CORS(app, origins=["http://localhost:8000", "https://example.com"]).
Default : '*'
• methods (list or string) --
The method or list of methods which the allowed origins are allowed to
access for non-simple requests.
Default : [GET, HEAD, POST, OPTIONS, PUT, PATCH, DELETE]
• expose_headers (list or string) --
The header or list which are safe to expose to the API of a CORS API
specification.
Default : None
• allow_headers (list, string or regex) --
The header or list of header field names which can be used when this
resource is accessed by allowed origins. The header(s) may be regular
expressions, case-sensitive strings, or else an asterisk.
Default : '*', allow all headers
• supports_credentials (bool) --
Allows users to make authenticated requests. If true, injects the
Access-Control-Allow-Credentials header in responses. This allows cookies
and credentials to be submitted across domains.
note This option cannot be used in conjunction with a '*' origin
Default : False
• max_age (timedelta, integer, string or None) --
The maximum time for which this CORS request maybe cached. This value is
set as the Access-Control-Max-Age header.
Default : None
• send_wildcard (bool) --
If True, and the origins parameter is *, a wildcard
Access-Control-Allow-Origin header is sent, rather than the request's
Origin header.
Default : False
• vary_header (bool) --
If True, the header Vary: Origin will be returned as per 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 cached.
If False, the Vary header will never be injected or altered.
Default : True
Decorator
If the CORS extension does not satisfy your needs, you may find the decorator useful. It
shares options with the extension, and should be simple to use.
flask_cors.cross_origin(*args, **kwargs)
This function is the decorator which is used to wrap a Flask route with. In the
simplest case, simply use the default parameters to allow all origins in what is
the most permissive configuration. If this method modifies state or performs
authentication which may be brute-forced, you should add some degree of protection,
such as Cross Site Request Forgery protection.
Parameters
• origins (list, string or regex) --
The origin, or list of origins to allow requests from. The origin(s) may
be regular expressions, case-sensitive strings, or else an asterisk
Default : '*'
• methods (list or string) --
The method or list of methods which the allowed origins are allowed to
access for non-simple requests.
Default : [GET, HEAD, POST, OPTIONS, PUT, PATCH, DELETE]
• expose_headers (list or string) --
The header or list which are safe to expose to the API of a CORS API
specification.
Default : None
• allow_headers (list, string or regex) --
The header or list of header field names which can be used when this
resource is accessed by allowed origins. The header(s) may be regular
expressions, case-sensitive strings, or else an asterisk.
Default : '*', allow all headers
• supports_credentials (bool) --
Allows users to make authenticated requests. If true, injects the
Access-Control-Allow-Credentials header in responses. This allows cookies
and credentials to be submitted across domains.
note This option cannot be used in conjunction with a '*' origin
Default : False
• max_age (timedelta, integer, string or None) --
The maximum time for which this CORS request maybe cached. This value is
set as the Access-Control-Max-Age header.
Default : None
• send_wildcard (bool) --
If True, and the origins parameter is *, a wildcard
Access-Control-Allow-Origin header is sent, rather than the request's
Origin header.
Default : False
• vary_header (bool) --
If True, the header Vary: Origin will be returned as per 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 cached.
If False, the Vary header will never be injected or altered.
Default : True
• automatic_options (bool) --
Only applies to the cross_origin decorator. If True, Flask-CORS will
override Flask's default OPTIONS handling to return CORS headers for
OPTIONS requests.
Default : True
Using CORS with cookies
By default, Flask-CORS does not allow cookies to be submitted across sites, since it has
potential security implications. If you wish to enable cross-site cookies, you may wish
to add some sort of CSRF protection to keep you and your users safe.
To allow cookies or authenticated requests to be made cross origins, simply set the
supports_credentials option to True. E.g.
from flask import Flask, session
from flask_cors import CORS
app = Flask(__name__)
CORS(app, supports_credentials=True)
@app.route("/")
def helloWorld():
return "Hello, %s" % session['username']
The above code enables Flask backend to accept cookies to be submitted from cross origin
sites. But if you are sending Xhr requests (ajax calls) to a cross-origin server, by
default chrome or any modern browser won't send cookies and session with the request. You
should use withCredentials = True while sending Xhr request to enable that. You should
keep in mind about the necessary security concerns. Related MDN doc:
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/withCredentials
Using CORS with Blueprints
Flask-CORS supports blueprints out of the box. Simply pass a blueprint instance to the
CORS extension, and everything will just work.
api_v1 = Blueprint('API_v1', __name__)
CORS(api_v1) # enable CORS on the API_v1 blue print
@api_v1.route("/api/v1/users/")
def list_users():
'''
Since the path matches the regular expression r'/api/*', this resource
automatically has CORS headers set. The expected result is as follows:
$ curl --include -X GET http://127.0.0.1:5000/api/v1/users/ \
--header Origin:www.examplesite.com
HTTP/1.0 200 OK
Access-Control-Allow-Headers: Content-Type
Access-Control-Allow-Origin: *
Content-Length: 21
Content-Type: application/json
Date: Sat, 09 Aug 2014 00:26:41 GMT
Server: Werkzeug/0.9.4 Python/2.7.8
{
"success": true
}
'''
return jsonify(user="joe")
@api_v1.route("/api/v1/users/create", methods=['POST'])
def create_user():
'''
Since the path matches the regular expression r'/api/*', this resource
automatically has CORS headers set.
Browsers will first make a preflight request to verify that the resource
allows cross-origin POSTs with a JSON Content-Type, which can be simulated
as:
$ curl --include -X OPTIONS http://127.0.0.1:5000/api/v1/users/create \
--header Access-Control-Request-Method:POST \
--header Access-Control-Request-Headers:Content-Type \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: text/html; charset=utf-8
Allow: POST, OPTIONS
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: Content-Type
Access-Control-Allow-Methods: DELETE, GET, HEAD, OPTIONS, PATCH, POST, PUT
Content-Length: 0
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:22 GMT
$ curl --include -X POST http://127.0.0.1:5000/api/v1/users/create \
--header Content-Type:application/json \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 21
Access-Control-Allow-Origin: *
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:04 GMT
{
"success": true
}
'''
return jsonify(success=True)
public_routes = Blueprint('public', __name__)
@public_routes.route("/")
def helloWorld():
'''
Since the path '/' does not match the regular expression r'/api/*',
this route does not have CORS headers set.
'''
return '''<h1>Hello CORS!</h1> Read about my spec at the
<a href="http://www.w3.org/TR/cors/">W3</a> Or, checkout my documentation
on <a href="https://github.com/corydolphin/flask-cors">Github</a>'''
logging.basicConfig(level=logging.INFO)
app = Flask('FlaskCorsBlueprintBasedExample')
app.register_blueprint(api_v1)
app.register_blueprint(public_routes)
if __name__ == "__main__":
app.run(debug=True)
Examples
Using the CORS extension
# One of the simplest configurations. Exposes all resources matching /api/* to
# CORS and allows the Content-Type header, which is necessary to POST JSON
# cross origin.
CORS(app, resources=r'/api/*')
@app.route("/")
def helloWorld():
"""
Since the path '/' does not match the regular expression r'/api/*',
this route does not have CORS headers set.
"""
return '''
<html>
<h1>Hello CORS!</h1>
<h3> End to end editable example with jquery! </h3>
<a class="jsbin-embed" href="http://jsbin.com/zazitas/embed?js,console">JS Bin on jsbin.com</a>
<script src="//static.jsbin.com/js/embed.min.js?3.35.12"></script>
</html>
'''
@app.route("/api/v1/users/")
def list_users():
"""
Since the path matches the regular expression r'/api/*', this resource
automatically has CORS headers set. The expected result is as follows:
$ curl --include -X GET http://127.0.0.1:5000/api/v1/users/ \
--header Origin:www.examplesite.com
HTTP/1.0 200 OK
Access-Control-Allow-Headers: Content-Type
Access-Control-Allow-Origin: *
Content-Length: 21
Content-Type: application/json
Date: Sat, 09 Aug 2014 00:26:41 GMT
Server: Werkzeug/0.9.4 Python/2.7.8
{
"success": true
}
"""
return jsonify(user="joe")
@app.route("/api/v1/users/create", methods=['POST'])
def create_user():
"""
Since the path matches the regular expression r'/api/*', this resource
automatically has CORS headers set.
Browsers will first make a preflight request to verify that the resource
allows cross-origin POSTs with a JSON Content-Type, which can be simulated
as:
$ curl --include -X OPTIONS http://127.0.0.1:5000/api/v1/users/create \
--header Access-Control-Request-Method:POST \
--header Access-Control-Request-Headers:Content-Type \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: text/html; charset=utf-8
Allow: POST, OPTIONS
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: Content-Type
Access-Control-Allow-Methods: DELETE, GET, HEAD, OPTIONS, PATCH, POST, PUT
Content-Length: 0
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:22 GMT
$ curl --include -X POST http://127.0.0.1:5000/api/v1/users/create \
--header Content-Type:application/json \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 21
Access-Control-Allow-Origin: *
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:04 GMT
{
"success": true
}
"""
return jsonify(success=True)
@app.route("/api/exception")
def get_exception():
"""
Since the path matches the regular expression r'/api/*', this resource
automatically has CORS headers set.
Browsers will first make a preflight request to verify that the resource
allows cross-origin POSTs with a JSON Content-Type, which can be simulated
as:
$ curl --include -X OPTIONS http://127.0.0.1:5000/api/exception \
--header Access-Control-Request-Method:POST \
--header Access-Control-Request-Headers:Content-Type \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: text/html; charset=utf-8
Allow: POST, OPTIONS
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: Content-Type
Access-Control-Allow-Methods: DELETE, GET, HEAD, OPTIONS, PATCH, POST, PUT
Content-Length: 0
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:22 GMT
"""
raise Exception("example")
@app.errorhandler(500)
def server_error(e):
logging.exception('An error occurred during a request. %s', e)
return "An internal error occurred", 500
if __name__ == "__main__":
app.run(debug=True)
Using the cross_origin decorator
@app.route("/", methods=['GET'])
@cross_origin()
def helloWorld():
'''
This view has CORS enabled for all domains, representing the simplest
configuration of view-based decoration. The expected result is as
follows:
$ curl --include -X GET http://127.0.0.1:5000/ \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: text/html; charset=utf-8
Content-Length: 184
Access-Control-Allow-Origin: *
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:29:56 GMT
<h1>Hello CORS!</h1> Read about my spec at the
<a href="http://www.w3.org/TR/cors/">W3</a> Or, checkout my documentation
on <a href="https://github.com/corydolphin/flask-cors">Github</a>
'''
return '''<h1>Hello CORS!</h1> Read about my spec at the
<a href="http://www.w3.org/TR/cors/">W3</a> Or, checkout my documentation
on <a href="https://github.com/corydolphin/flask-cors">Github</a>'''
@app.route("/api/v1/users/create", methods=['GET', 'POST'])
@cross_origin(allow_headers=['Content-Type'])
def cross_origin_json_post():
'''
This view has CORS enabled for all domains, and allows browsers
to send the Content-Type header, allowing cross domain AJAX POST
requests.
Browsers will first make a preflight request to verify that the resource
allows cross-origin POSTs with a JSON Content-Type, which can be simulated
as:
$ curl --include -X OPTIONS http://127.0.0.1:5000/api/v1/users/create \
--header Access-Control-Request-Method:POST \
--header Access-Control-Request-Headers:Content-Type \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: text/html; charset=utf-8
Allow: POST, OPTIONS
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: Content-Type
Access-Control-Allow-Methods: DELETE, GET, HEAD, OPTIONS, PATCH, POST, PUT
Content-Length: 0
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:22 GMT
$ curl --include -X POST http://127.0.0.1:5000/api/v1/users/create \
--header Content-Type:application/json \
--header Origin:www.examplesite.com
>> HTTP/1.0 200 OK
Content-Type: application/json
Content-Length: 21
Access-Control-Allow-Origin: *
Server: Werkzeug/0.9.6 Python/2.7.9
Date: Sat, 31 Jan 2015 22:25:04 GMT
{
"success": true
}
'''
return jsonify(success=True)
if __name__ == "__main__":
app.run(debug=True)
AUTHOR
Cory Dolphin
COPYRIGHT
2023, Cory Dolphin