去掉django rest framework强制的csrf检查

近期的项目，前端的js是在localhost上跑的，然后向我们后端的开发服务器进行请求。但是突然前端说所有的post请求都报csrf校验错误了，甚是奇怪，之前为了开发方便已经把django的csrf middleware注释掉了啊，为什么还会错误，由于返回值格式还是django rest的通用格式，肯定问题是出在这里面，于是翻了一下它的源代码看了看。

from django.middleware.csrf import CsrfViewMiddleware

class CSRFCheck(CsrfViewMiddleware):
def _reject(self, request, reason):
# Return the failure reason instead of an HttpResponse
return reason

class SessionAuthentication(BaseAuthentication):
“””
Use Django’s session framework for authentication.
“”“

def authenticate(self, request):
    """
    Returns a `User` if the request session currently has a logged in user.
    Otherwise returns `None`.
    """

    # Get the underlying HttpRequest object
    request = request._request
    user = getattr(request, 'user', None)

    # Unauthenticated, CSRF validation not required
    if not user or not user.is_active:
        return None

    self.enforce_csrf(request)

    # CSRF passed with authenticated user
    return (user, None)

def enforce_csrf(self, request):
    """
    Enforce CSRF validation for session based authentication.
    """
    reason = CSRFCheck().process_view(request, None, (), {})
    if reason:
        # CSRF failed, bail with explicit error message
        raise exceptions.PermissionDenied('CSRF Failed: %s' % reason)

原来是这样，最近给系统增加了用户登陆功能，使用的就是SessionAuthorization和TokenAuthorization，然后在SessionAuthorization中调用了self.enforce_csrf(request)而这个调用的又是上面的CSRFCheck，这个类是重载了django里面的csrf middleware，而且没发现有地方可以关掉这个功能，即使在django里面去掉这个middleware，但是这个还是会调用的。

那怎么去掉这个功能呢，我们现在就是要进行跨域请求。

最简单了，直接注释掉上面的self.enforce_csrf(request)这一行代码就行了或者在设置中添加一项，比如改成
GLOBAL_CSRF_CHECK = True
if GLOBAL_CSRF_CHECK：
self.enforce_csrf(request)
我们继续看源代码，到middleware的代码里面去。
class CsrfViewMiddleware(object):
“””
Middleware that requires a present and correct csrfmiddlewaretoken
for POST requests that have a CSRF cookie, and sets an outgoing
CSRF cookie.

This middleware should be used in conjunction with the csrf_token template
tag.
"""
# The _accept and _reject methods currently only exist for the sake of the
# requires_csrf_token decorator.
def _accept(self, request):
    # Avoid checking the request twice by adding a custom attribute to
    # request.  This will be relevant when both decorator and middleware
    # are used.
    request.csrf_processing_done = True
    return None

def _reject(self, request, reason):
    logger.warning('Forbidden (%s): %s',
                   reason, request.path,
        extra={
            'status_code': 403,
            'request': request,
        }
    )
    return _get_failure_view()(request, reason=reason)

def process_view(self, request, callback, callback_args, callback_kwargs):

    if getattr(request, 'csrf_processing_done', False):
        return None

    try:
        csrf_token = _sanitize_token(
            request.COOKIES[settings.CSRF_COOKIE_NAME])
        # Use same token next time
        request.META['CSRF_COOKIE'] = csrf_token
    except KeyError:
        csrf_token = None
        # Generate token and store it in the request, so it's
        # available to the view.
        request.META["CSRF_COOKIE"] = _get_new_csrf_key()

    # Wait until request.META["CSRF_COOKIE"] has been manipulated before
    # bailing out, so that get_token still works
    if getattr(callback, 'csrf_exempt', False):
        return None

    # Assume that anything not defined as 'safe' by RFC2616 needs protection
    if request.method not in ('GET', 'HEAD', 'OPTIONS', 'TRACE'):
        if getattr(request, '_dont_enforce_csrf_checks', False):
            # Mechanism to turn off CSRF checks for test suite.
            # It comes after the creation of CSRF cookies, so that
            # everything else continues to work exactly the same
            # (e.g. cookies are sent, etc.), but before any
            # branches that call reject().
            return self._accept(request)

        if request.is_secure():
            # Suppose user visits http://example.com/
            # An active network attacker (man-in-the-middle, MITM) sends a
            # POST form that targets https://example.com/detonate-bomb/ and
            # submits it via JavaScript.
            #
            # The attacker will need to provide a CSRF cookie and token, but
            # that's no problem for a MITM and the session-independent
            # nonce we're using. So the MITM can circumvent the CSRF
            # protection. This is true for any HTTP connection, but anyone
            # using HTTPS expects better! For this reason, for
            # https://example.com/ we need additional protection that treats
            # http://example.com/ as completely untrusted. Under HTTPS,
            # Barth et al. found that the Referer header is missing for
            # same-domain requests in only about 0.2% of cases or less, so
            # we can use strict Referer checking.
            referer = request.META.get('HTTP_REFERER')
            if referer is None:
                return self._reject(request, REASON_NO_REFERER)

            # Note that request.get_host() includes the port.
            good_referer = 'https://%s/' % request.get_host()
            if not same_origin(referer, good_referer):
                reason = REASON_BAD_REFERER % (referer, good_referer)
                return self._reject(request, reason)

        if csrf_token is None:
            # No CSRF cookie. For POST requests, we insist on a CSRF cookie,
            # and in this way we can avoid all CSRF attacks, including login
            # CSRF.
            return self._reject(request, REASON_NO_CSRF_COOKIE)

        # Check non-cookie token for match.
        request_csrf_token = ""
        if request.method == "POST":
            request_csrf_token = request.POST.get('csrfmiddlewaretoken', '')

        if request_csrf_token == "":
            # Fall back to X-CSRFToken, to make things easier for AJAX,
            # and possible for PUT/DELETE.
            request_csrf_token = request.META.get('HTTP_X_CSRFTOKEN', '')

        if not constant_time_compare(request_csrf_token, csrf_token):
            return self._reject(request, REASON_BAD_TOKEN)

    return self._accept(request)

def process_response(self, request, response):
    if getattr(response, 'csrf_processing_done', False):
        return response

    # If CSRF_COOKIE is unset, then CsrfViewMiddleware.process_view was
    # never called, probaby because a request middleware returned a response
    # (for example, contrib.auth redirecting to a login page).
    if request.META.get("CSRF_COOKIE") is None:
        return response

    if not request.META.get("CSRF_COOKIE_USED", False):
        return response

    # Set the CSRF cookie even if it's already set, so we renew
    # the expiry timer.
    response.set_cookie(settings.CSRF_COOKIE_NAME,
                        request.META["CSRF_COOKIE"],
                        max_age = 60 * 60 * 24 * 7 * 52,
                        domain=settings.CSRF_COOKIE_DOMAIN,
                        path=settings.CSRF_COOKIE_PATH,
                        secure=settings.CSRF_COOKIE_SECURE,
                        httponly=settings.CSRF_COOKIE_HTTPONLY
                        )
    # Content varies with the CSRF cookie, so set the Vary header.
    patch_vary_headers(response, ('Cookie',))
    response.csrf_processing_done = True
    return response

里面主要有两个函数，一个是process view，另一个是process response。这里就不得不说django middleware的工作原理了。

https://docs.djangoproject.com/en/1.6/topics/http/middleware/

process_request() is called on each request, before Django decides which view to execute.

process_view() is called just before Django calls the view.

process_response() is called on all responses before they’re returned to the browser.
所以这个middleware的process view会在请求到达view函数之前被调用，可以理解为一个过滤器吧。

if request.method not in (‘GET’, ‘HEAD’, ‘OPTIONS’, ‘TRACE’):
if getattr(request, ‘_dont_enforce_csrf_checks’, False):
return self._accept(request)
这里request里面有_dont_enforce_csrf_checks就直接进入view了，没有下面的检查了。所以我们只要自己给request添加一个这样的属性就好了。最直接的方法还是去写一个middleware啊，哈哈。

代码很简单

class DisableCSRFCheck(object):
def process_request(self, request):
setattr(request, ‘_dont_enforce_csrf_checks’, True)