466 lines
17 KiB
Python
466 lines
17 KiB
Python
# Copyright 2015 Google Inc.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from collections import OrderedDict
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import flask
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DENY = 'DENY'
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SAMEORIGIN = 'SAMEORIGIN'
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ALLOW_FROM = 'ALLOW-FROM'
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ONE_YEAR_IN_SECS = 31556926
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DEFAULT_REFERRER_POLICY = 'strict-origin-when-cross-origin'
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DEFAULT_CSP_POLICY = {
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'default-src': '\'self\'',
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'object-src': '\'none\'',
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}
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DEFAULT_SESSION_COOKIE_SAMESITE = "Lax"
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GOOGLE_CSP_POLICY = {
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# Fonts from fonts.google.com
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'font-src': '\'self\' themes.googleusercontent.com *.gstatic.com',
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# <iframe> based embedding for Maps and Youtube.
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'frame-src': '\'self\' www.google.com www.youtube.com',
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# Assorted Google-hosted Libraries/APIs.
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'script-src': '\'self\' ajax.googleapis.com *.googleanalytics.com '
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'*.google-analytics.com',
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# Used by generated code from http://www.google.com/fonts
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'style-src': '\'self\' ajax.googleapis.com fonts.googleapis.com '
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'*.gstatic.com',
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'object-src': '\'none\'',
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'default-src': '\'self\' *.gstatic.com',
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}
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DEFAULT_PERMISSIONS_POLICY = {
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# Disable Topics API
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'browsing-topics': '()'
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}
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DEFAULT_DOCUMENT_POLICY = {
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}
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DEFAULT_FEATURE_POLICY = {
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}
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NONCE_LENGTH = 32
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class Talisman(object):
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"""
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Talisman is a Flask extension for HTTP security headers.
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"""
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def __init__(self, app=None, **kwargs):
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if app is not None:
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self.init_app(app, **kwargs)
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def init_app(
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self,
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app,
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feature_policy=DEFAULT_FEATURE_POLICY,
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permissions_policy=DEFAULT_PERMISSIONS_POLICY,
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document_policy=DEFAULT_DOCUMENT_POLICY,
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force_https=True,
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force_https_permanent=False,
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force_file_save=False,
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frame_options=SAMEORIGIN,
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frame_options_allow_from=None,
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strict_transport_security=True,
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strict_transport_security_preload=False,
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strict_transport_security_max_age=ONE_YEAR_IN_SECS,
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strict_transport_security_include_subdomains=True,
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content_security_policy=DEFAULT_CSP_POLICY,
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content_security_policy_report_uri=None,
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content_security_policy_report_only=False,
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content_security_policy_nonce_in=None,
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referrer_policy=DEFAULT_REFERRER_POLICY,
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session_cookie_secure=True,
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session_cookie_http_only=True,
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session_cookie_samesite=DEFAULT_SESSION_COOKIE_SAMESITE,
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x_content_type_options=True,
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x_xss_protection=False):
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"""
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Initialization.
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Args:
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app: A Flask application.
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feature_policy: A string or dictionary describing the
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feature policy for the response.
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permissions_policy: A string or dictionary describing the
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permissions policy for the response.
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document_policy: A string or dictionary describing the
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document policy for the response.
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force_https: Redirects non-http requests to https, disabled in
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debug mode.
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force_https_permanent: Uses 301 instead of 302 redirects.
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frame_options: Sets the X-Frame-Options header, defaults to
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SAMEORIGIN.
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frame_options_allow_from: Used when frame_options is set to
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ALLOW_FROM and is a string of domains to allow frame embedding.
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strict_transport_security: Sets HSTS headers.
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strict_transport_security_preload: Enables HSTS preload. See
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https://hstspreload.org.
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strict_transport_security_max_age: How long HSTS headers are
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honored by the browser.
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strict_transport_security_include_subdomains: Whether to include
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all subdomains when setting HSTS.
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content_security_policy: A string or dictionary describing the
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content security policy for the response.
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content_security_policy_report_uri: A string indicating the report
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URI used for CSP violation reports
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content_security_policy_report_only: Whether to set the CSP header
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as "report-only", which disables the enforcement by the browser
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and requires a "report-uri" parameter with a backend to receive
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the POST data
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content_security_policy_nonce_in: A list of csp sections to include
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a per-request nonce value in
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referrer_policy: A string describing the referrer policy for the
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response.
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session_cookie_secure: Forces the session cookie to only be sent
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over https. Disabled in debug mode.
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session_cookie_http_only: Prevents JavaScript from reading the
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session cookie.
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session_cookie_samesite: Sets samesite parameter on session cookie
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force_file_save: Prevents the user from opening a file download
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directly on >= IE 8
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x_content_type_options: Prevents MIME type sniffing
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x_xss_protection: Prevents the page from loading when the browser
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detects reflected cross-site scripting attacks
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See README.rst for a detailed description of each option.
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"""
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if isinstance(feature_policy, dict):
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self.feature_policy = OrderedDict(feature_policy)
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else:
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self.feature_policy = feature_policy
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if isinstance(permissions_policy, dict):
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self.permissions_policy = OrderedDict(permissions_policy)
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else:
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self.permissions_policy = permissions_policy
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if isinstance(document_policy, dict):
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self.document_policy = OrderedDict(document_policy)
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else:
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self.document_policy = document_policy
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self.force_https = force_https
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self.force_https_permanent = force_https_permanent
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self.frame_options = frame_options
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self.frame_options_allow_from = frame_options_allow_from
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self.strict_transport_security = strict_transport_security
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self.strict_transport_security_preload = \
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strict_transport_security_preload
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self.strict_transport_security_max_age = \
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strict_transport_security_max_age
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self.strict_transport_security_include_subdomains = \
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strict_transport_security_include_subdomains
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if isinstance(content_security_policy, dict):
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self.content_security_policy = OrderedDict(content_security_policy)
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else:
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self.content_security_policy = content_security_policy
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self.content_security_policy_report_uri = \
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content_security_policy_report_uri
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self.content_security_policy_report_only = \
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content_security_policy_report_only
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if self.content_security_policy_report_only and \
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self.content_security_policy_report_uri is None:
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raise ValueError(
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'Setting content_security_policy_report_only to True also '
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'requires a URI to be specified in '
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'content_security_policy_report_uri')
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self.content_security_policy_nonce_in = (
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content_security_policy_nonce_in or []
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)
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app.jinja_env.globals['csp_nonce'] = self._get_nonce
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self.referrer_policy = referrer_policy
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self.session_cookie_secure = session_cookie_secure
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app.config['SESSION_COOKIE_SAMESITE'] = session_cookie_samesite
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if session_cookie_http_only:
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app.config['SESSION_COOKIE_HTTPONLY'] = True
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self.force_file_save = force_file_save
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self.x_content_type_options = x_content_type_options
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self.x_xss_protection = x_xss_protection
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self.app = app
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app.before_request(self._force_https)
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app.before_request(self._make_nonce)
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app.after_request(self._set_response_headers)
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def _get_local_options(self):
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view_function = flask.current_app.view_functions.get(
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flask.request.endpoint)
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view_options = getattr(
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view_function, 'talisman_view_options', {})
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view_options.setdefault('force_https', self.force_https)
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view_options.setdefault('frame_options', self.frame_options)
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view_options.setdefault(
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'frame_options_allow_from', self.frame_options_allow_from)
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view_options.setdefault(
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'content_security_policy', self.content_security_policy)
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view_options.setdefault(
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'content_security_policy_nonce_in',
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self.content_security_policy_nonce_in)
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view_options.setdefault(
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'permissions_policy', self.permissions_policy)
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view_options.setdefault(
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'document_policy', self.document_policy)
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view_options.setdefault(
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'feature_policy', self.feature_policy
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)
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return view_options
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def _force_https(self):
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"""Redirect any non-https requests to https.
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Based largely on flask-sslify.
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"""
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if self.session_cookie_secure:
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if not self.app.debug:
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self.app.config['SESSION_COOKIE_SECURE'] = True
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criteria = [
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self.app.debug,
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flask.request.is_secure,
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flask.request.headers.get('X-Forwarded-Proto', 'http') == 'https',
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]
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local_options = self._get_local_options()
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if local_options['force_https'] and not any(criteria):
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if flask.request.url.startswith('http://'):
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url = flask.request.url.replace('http://', 'https://', 1)
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code = 302
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if self.force_https_permanent:
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code = 301
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r = flask.redirect(url, code=code)
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return r
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def _set_response_headers(self, response):
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"""Applies all configured headers to the given response."""
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options = self._get_local_options()
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self._set_feature_policy_headers(response.headers, options)
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self._set_permissions_policy_headers(response.headers, options)
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self._set_document_policy_headers(response.headers, options)
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self._set_frame_options_headers(response.headers, options)
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self._set_content_security_policy_headers(response.headers, options)
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self._set_hsts_headers(response.headers)
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self._set_referrer_policy_headers(response.headers)
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return response
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def _make_nonce(self):
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local_options = self._get_local_options()
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if (
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local_options['content_security_policy'] and
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local_options['content_security_policy_nonce_in'] and
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not getattr(flask.request, 'csp_nonce', None)):
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flask.request.csp_nonce = get_random_string(NONCE_LENGTH)
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def _get_nonce(self):
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return getattr(flask.request, 'csp_nonce', '')
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def _parse_structured_header_policy(self, policy):
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if isinstance(policy, str):
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return policy
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policies = []
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for section, content in policy.items():
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policy_part = '{}={}'.format(section, content)
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policies.append(policy_part)
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policy = ', '.join(policies)
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return policy
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def _parse_policy(self, policy):
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local_options = self._get_local_options()
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if isinstance(policy, str):
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# parse the string into a policy dict
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policy_string = policy
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policy = OrderedDict()
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for policy_part in policy_string.split(';'):
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policy_parts = policy_part.strip().split(' ')
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policy[policy_parts[0]] = " ".join(policy_parts[1:])
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policies = []
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for section, content in policy.items():
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if not isinstance(content, str):
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content = ' '.join(content)
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policy_part = '{} {}'.format(section, content)
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if (
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hasattr(flask.request, 'csp_nonce') and
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section in local_options['content_security_policy_nonce_in']):
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policy_part += " 'nonce-{}'".format(flask.request.csp_nonce)
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policies.append(policy_part)
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policy = '; '.join(policies)
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return policy
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def _set_feature_policy_headers(self, headers, options):
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if not options['feature_policy']:
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return
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policy = options['feature_policy']
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policy = self._parse_policy(policy)
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headers['Feature-Policy'] = policy
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def _set_permissions_policy_headers(self, headers, options):
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if not options['permissions_policy']:
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return
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policy = options['permissions_policy']
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policy = self._parse_structured_header_policy(policy)
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headers['Permissions-Policy'] = policy
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def _set_document_policy_headers(self, headers, options):
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if not options['document_policy']:
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return
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policy = options['document_policy']
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policy = self._parse_structured_header_policy(policy)
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headers['Document-Policy'] = policy
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def _set_frame_options_headers(self, headers, options):
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if not options['frame_options']:
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return
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headers['X-Frame-Options'] = options['frame_options']
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if options['frame_options'] == ALLOW_FROM:
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headers['X-Frame-Options'] += " {}".format(
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options['frame_options_allow_from'])
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def _set_content_security_policy_headers(self, headers, options):
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if self.x_xss_protection:
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headers['X-XSS-Protection'] = '1; mode=block'
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if self.x_content_type_options:
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headers['X-Content-Type-Options'] = 'nosniff'
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if self.force_file_save:
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headers['X-Download-Options'] = 'noopen'
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if not options['content_security_policy']:
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return
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policy = options['content_security_policy']
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policy = self._parse_policy(policy)
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if self.content_security_policy_report_uri and \
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'report-uri' not in policy:
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policy += '; report-uri ' + self.content_security_policy_report_uri
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csp_header = 'Content-Security-Policy'
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if self.content_security_policy_report_only:
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csp_header += '-Report-Only'
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headers[csp_header] = policy
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def _set_hsts_headers(self, headers):
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criteria = [
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flask.request.is_secure,
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flask.request.headers.get('X-Forwarded-Proto', 'http') == 'https',
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]
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if not self.strict_transport_security or not any(criteria):
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return
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value = 'max-age={}'.format(self.strict_transport_security_max_age)
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if self.strict_transport_security_include_subdomains:
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value += '; includeSubDomains'
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if self.strict_transport_security_preload:
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value += '; preload'
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headers['Strict-Transport-Security'] = value
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def _set_referrer_policy_headers(self, headers):
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headers['Referrer-Policy'] = self.referrer_policy
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def __call__(self, **kwargs):
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"""Use talisman as a decorator to configure options for a particular
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view.
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Only force_https, frame_options, frame_options_allow_from,
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content_security_policy, content_security_policy_nonce_in
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and feature_policy can be set on a per-view basis.
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Example:
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app = Flask(__name__)
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talisman = Talisman(app)
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@app.route('/normal')
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def normal():
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return 'Normal'
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@app.route('/embeddable')
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@talisman(frame_options=ALLOW_FROM, frame_options_allow_from='*')
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def embeddable():
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return 'Embeddable'
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"""
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def decorator(f):
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setattr(f, 'talisman_view_options', kwargs)
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return f
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return decorator
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try:
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import secrets
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def get_random_string(length): # pragma: no cover
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# Note token_urlsafe returns a 'length'-byte string which is then
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# base64 encoded so is longer than length, so only return last
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# 'length' characters.
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return secrets.token_urlsafe(length)[:length]
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except ImportError: # pragma: no cover
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import random
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import string
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rnd = random.SystemRandom()
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def get_random_string(length):
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allowed_chars = (
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string.ascii_lowercase +
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string.ascii_uppercase +
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string.digits)
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return ''.join(
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rnd.choice(allowed_chars)
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for _ in range(length))
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