Unauthenticated requests - 401 vs 403 responses

docs/api-guide/authentication.md

@@ -8,25 +8,33 @@
 
 Authentication is the mechanism of associating an incoming request with a set of identifying credentials, such as the user the request came from, or the token that it was signed with.  The [permission] and [throttling] policies can then use those credentials to determine if the request should be permitted.
 
-REST framework provides a number of authentication policies out of the box, and also allows you to implement custom policies.
+REST framework provides a number of authentication schemes out of the box, and also allows you to implement custom schemes.
 
 Authentication will run the first time either the `request.user` or `request.auth` properties are accessed, and determines how those properties are initialized.
 
 The `request.user` property will typically be set to an instance of the `contrib.auth` package's `User` class.
 
 The `request.auth` property is used for any additional authentication information, for example, it may be used to represent an authentication token that the request was signed with.
 
+---
+
+**Note:** Don't forget that **authentication by itself won't allow or disallow an incoming request**, it simply identifies the credentials that the request was made with.
+
+For information on how to setup the permission polices for your API please see the [permissions documentation][permission].
+
+---
+
 ## How authentication is determined
 
-The authentication policy is always defined as a list of classes.  REST framework will attempt to authenticate with each class in the list, and will set `request.user` and `request.auth` using the return value of the first class that successfully authenticates.
+The authentication schemes are always defined as a list of classes.  REST framework will attempt to authenticate with each class in the list, and will set `request.user` and `request.auth` using the return value of the first class that successfully authenticates.
 
 If no class authenticates, `request.user` will be set to an instance of `django.contrib.auth.models.AnonymousUser`, and `request.auth` will be set to `None`.
 
 The value of `request.user` and `request.auth` for unauthenticated requests can be modified using the `UNAUTHENTICATED_USER` and `UNAUTHENTICATED_TOKEN` settings.
 
-## Setting the authentication policy
+## Setting the authentication scheme
 
-The default authentication policy may be set globally, using the `DEFAULT_AUTHENTICATION_CLASSES` setting.  For example.
+The default authentication schemes may be set globally, using the `DEFAULT_AUTHENTICATION` setting.  For example.
 
     REST_FRAMEWORK = {
         'DEFAULT_AUTHENTICATION_CLASSES': (
@@ -35,7 +43,7 @@ The default authentication policy may be set globally, using the `DEFAULT_AUTHEN
         )
     }
 
-You can also set the authentication policy on a per-view basis, using the `APIView` class based views.
+You can also set the authentication scheme on a per-view basis, using the `APIView` class based views.
 
     class ExampleView(APIView):
         authentication_classes = (SessionAuthentication, BasicAuthentication)
@@ -60,6 +68,19 @@ Or, if you're using the `@api_view` decorator with function based views.
         }
         return Response(content)
 
+## Unauthorized and Forbidden responses
+
+When an unauthenticated request is denied permission there are two different error codes that may be appropriate.
+
+* [HTTP 401 Unauthorized][http401]
+* [HTTP 403 Permission Denied][http403]
+
+HTTP 401 responses must always include a `WWW-Authenticate` header, that instructs the client how to authenticate.  HTTP 403 responses do not include the `WWW-Authenticate` header.
+
+The kind of response that will be used depends on the authentication scheme.  Although multiple authentication schemes may be in use, only one scheme may be used to determine the type of response.  **The first authentication class set on the view is used when determining the type of response**.
+
+Note that when a request may successfully authenticate, but still be denied permission to perform the request, in which case a `403 Permission Denied` response will always be used, regardless of the authentication scheme.
+
 ## Apache mod_wsgi specific configuration
 
 Note that if deploying to [Apache using mod_wsgi][mod_wsgi_official], the authorization header is not passed through to a WSGI application by default, as it is assumed that authentication will be handled by Apache, rather than at an application level.
@@ -69,24 +90,30 @@ If you are deploying to Apache, and using any non-session based authentication,
     # this can go in either server config, virtual host, directory or .htaccess 
     WSGIPassAuthorization On
 
+---
+
 # API Reference
 
 ## BasicAuthentication
 
-This policy uses [HTTP Basic Authentication][basicauth], signed against a user's username and password.  Basic authentication is generally only appropriate for testing.
+This authentication scheme uses [HTTP Basic Authentication][basicauth], signed against a user's username and password.  Basic authentication is generally only appropriate for testing.
 
 If successfully authenticated, `BasicAuthentication` provides the following credentials.
 
 * `request.user` will be a Django `User` instance.
 * `request.auth` will be `None`.
 
+Unauthenticated responses that are denied permission will result in an `HTTP 401 Unauthorized` response with an appropriate WWW-Authenticate header.  For example:
+
+    WWW-Authenticate: Basic realm="api"
+
 **Note:** If you use `BasicAuthentication` in production you must ensure that your API is only available over `https` only.  You should also ensure that your API clients will always re-request the username and password at login, and will never store those details to persistent storage.
 
 ## TokenAuthentication
 
-This policy uses a simple token-based HTTP Authentication scheme.  Token authentication is appropriate for client-server setups, such as native desktop and mobile clients.
+This authentication scheme uses a simple token-based HTTP Authentication scheme.  Token authentication is appropriate for client-server setups, such as native desktop and mobile clients.
 
-To use the `TokenAuthentication` policy, include `rest_framework.authtoken` in your `INSTALLED_APPS` setting.
+To use the `TokenAuthentication` scheme, include `rest_framework.authtoken` in your `INSTALLED_APPS` setting.
 
 You'll also need to create tokens for your users.
 
@@ -104,8 +131,13 @@ If successfully authenticated, `TokenAuthentication` provides the following cred
 * `request.user` will be a Django `User` instance.
 * `request.auth` will be a `rest_framework.authtoken.models.BasicToken` instance.
 
+Unauthenticated responses that are denied permission will result in an `HTTP 401 Unauthorized` response with an appropriate WWW-Authenticate header.  For example:
+
+    WWW-Authenticate: Token
+
 **Note:** If you use `TokenAuthentication` in production you must ensure that your API is only available over `https` only.
 
+=======
 If you want every user to have an automatically generated Token, you can simply catch the User's `post_save` signal.
 
     @receiver(post_save, sender=User)
@@ -136,20 +168,35 @@ The `obtain_auth_token` view will return a JSON response when valid `username` a
 
 ## SessionAuthentication
 
-This policy uses Django's default session backend for authentication.  Session authentication is appropriate for AJAX clients that are running in the same session context as your website.
+This authentication scheme uses Django's default session backend for authentication.  Session authentication is appropriate for AJAX clients that are running in the same session context as your website.
 
 If successfully authenticated, `SessionAuthentication` provides the following credentials.
 
 * `request.user` will be a Django `User` instance.
 * `request.auth` will be `None`.
 
+Unauthenticated responses that are denied permission will result in an `HTTP 403 Forbidden` response.
+
 If you're using an AJAX style API with SessionAuthentication, you'll need to make sure you include a valid CSRF token for any "unsafe" HTTP method calls, such as `PUT`, `POST` or `DELETE` requests.  See the [Django CSRF documentation][csrf-ajax] for more details.
 
 # Custom authentication
 
-To implement a custom authentication policy, subclass `BaseAuthentication` and override the `.authenticate(self, request)` method.  The method should return a two-tuple of `(user, auth)` if authentication succeeds, or `None` otherwise.
+To implement a custom authentication scheme, subclass `BaseAuthentication` and override the `.authenticate(self, request)` method.  The method should return a two-tuple of `(user, auth)` if authentication succeeds, or `None` otherwise.
+
+In some circumstances instead of returning `None`, you may want to raise an `AuthenticationFailed` exception from the `.authenticate()` method.
+
+Typically the approach you should take is:
+
+* If authentication is not attempted, return `None`.  Any other authentication schemes also in use will still be checked.
+* If authentication is attempted but fails, raise a `AuthenticationFailed` exception.  An error response will be returned immediately, without checking any other authentication schemes.
+
+You *may* also override the `.authentication_header(self, request)` method.  If implemented, it should return a string that will be used as the value of the `WWW-Authenticate` header in a `HTTP 401 Unauthorized` response.
+
+If the `.authentication_header()` method is not overridden, the authentication scheme will return `HTTP 403 Forbidden` responses when an unauthenticated request is denied access.
 
 [cite]: http://jacobian.org/writing/rest-worst-practices/
+[http401]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.2
+[http403]: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.4
 [basicauth]: http://tools.ietf.org/html/rfc2617
 [oauth]: http://oauth.net/2/
 [permission]: permissions.md

docs/api-guide/exceptions.md

@@ -53,11 +53,27 @@ Raised if the request contains malformed data when accessing `request.DATA` or `
 
 By default this exception results in a response with the HTTP status code "400 Bad Request".
 
+## AuthenticationFailed
+
+**Signature:** `AuthenticationFailed(detail=None)`
+
+Raised when an incoming request includes incorrect authentication.
+
+By default this exception results in a response with the HTTP status code "401 Unauthenticated", but it may also result in a "403 Forbidden" response, depending on the authentication scheme in use.  See the [authentication documentation][authentication] for more details.
+
+## NotAuthenticated
+
+**Signature:** `NotAuthenticated(detail=None)`
+
+Raised when an unauthenticated request fails the permission checks.
+
+By default this exception results in a response with the HTTP status code "401 Unauthenticated", but it may also result in a "403 Forbidden" response, depending on the authentication scheme in use.  See the [authentication documentation][authentication] for more details.
+
 ## PermissionDenied
 
 **Signature:** `PermissionDenied(detail=None)`
 
-Raised when an incoming request fails the permission checks.
+Raised when an authenticated request fails the permission checks.
 
 By default this exception results in a response with the HTTP status code "403 Forbidden".
 
@@ -86,3 +102,4 @@ Raised when an incoming request fails the throttling checks.
 By default this exception results in a response with the HTTP status code "429 Too Many Requests".
 
 [cite]: http://www.doughellmann.com/articles/how-tos/python-exception-handling/index.html
+[authentication]: authentication.md

rest_framework/authentication.py

@@ -21,32 +21,46 @@ def authenticate(self, request):
         """
         raise NotImplementedError(".authenticate() must be overridden.")
 
+    def authenticate_header(self, request):
+        """
+        Return a string to be used as the value of the `WWW-Authenticate`
+        header in a `401 Unauthenticated` response, or `None` if the
+        authentication scheme should return `403 Permission Denied` responses.
+        """
+        pass
+
 
 class BasicAuthentication(BaseAuthentication):
     """
     HTTP Basic authentication against username/password.
     """
+    www_authenticate_realm = 'api'
 
     def authenticate(self, request):
         """
         Returns a `User` if a correct username and password have been supplied
         using HTTP Basic authentication.  Otherwise returns `None`.
         """
-        if 'HTTP_AUTHORIZATION' in request.META:
-            auth = request.META['HTTP_AUTHORIZATION'].split()
-            if len(auth) == 2 and auth[0].lower() == "basic":
-                try:
-                    auth_parts = base64.b64decode(auth[1]).partition(':')
-                except TypeError:
-                    return None
-
-                try:
-                    userid = smart_unicode(auth_parts[0])
-                    password = smart_unicode(auth_parts[2])
-                except DjangoUnicodeDecodeError:
-                    return None
-
-                return self.authenticate_credentials(userid, password)
+        auth = request.META.get('HTTP_AUTHORIZATION', '').split()
+
+        if not auth or auth[0].lower() != "basic":
+            return None
+
+        if len(auth) != 2:
+            raise exceptions.AuthenticationFailed('Invalid basic header')
+
+        try:
+            auth_parts = base64.b64decode(auth[1]).partition(':')
+        except TypeError:
+            raise exceptions.AuthenticationFailed('Invalid basic header')
+
+        try:
+            userid = smart_unicode(auth_parts[0])
+            password = smart_unicode(auth_parts[2])
+        except DjangoUnicodeDecodeError:
+            raise exceptions.AuthenticationFailed('Invalid basic header')
+
+        return self.authenticate_credentials(userid, password)
 
     def authenticate_credentials(self, userid, password):
         """
@@ -55,6 +69,10 @@ def authenticate_credentials(self, userid, password):
         user = authenticate(username=userid, password=password)
         if user is not None and user.is_active:
             return (user, None)
+        raise exceptions.AuthenticationFailed('Invalid username/password')
+
+    def authenticate_header(self, request):
+        return 'Basic realm="%s"' % self.www_authenticate_realm
 
 
 class SessionAuthentication(BaseAuthentication):
@@ -74,7 +92,7 @@ def authenticate(self, request):
 
         # Unauthenticated, CSRF validation not required
         if not user or not user.is_active:
-            return
+            return None
 
         # Enforce CSRF validation for session based authentication.
         class CSRFCheck(CsrfViewMiddleware):
@@ -85,7 +103,7 @@ def _reject(self, request, reason):
         reason = CSRFCheck().process_view(http_request, None, (), {})
         if reason:
             # CSRF failed, bail with explicit error message
-            raise exceptions.PermissionDenied('CSRF Failed: %s' % reason)
+            raise exceptions.AuthenticationFailed('CSRF Failed: %s' % reason)
 
         # CSRF passed with authenticated user
         return (user, None)
@@ -112,14 +130,26 @@ class TokenAuthentication(BaseAuthentication):
     def authenticate(self, request):
         auth = request.META.get('HTTP_AUTHORIZATION', '').split()
 
-        if len(auth) == 2 and auth[0].lower() == "token":
-            key = auth[1]
-            try:
-                token = self.model.objects.get(key=key)
-            except self.model.DoesNotExist:
-                return None
+        if not auth or auth[0].lower() != "token":
+            return None
+
+        if len(auth) != 2:
+            raise exceptions.AuthenticationFailed('Invalid token header')
+
+        return self.authenticate_credentials(auth[1])
+
+    def authenticate_credentials(self, key):
+        try:
+            token = self.model.objects.get(key=key)
+        except self.model.DoesNotExist:
+            raise exceptions.AuthenticationFailed('Invalid token')
+
+        if token.user.is_active:
+            return (token.user, token)
+        raise exceptions.AuthenticationFailed('User inactive or deleted')
+
+    def authenticate_header(self, request):
+        return 'Token'
 
-            if token.user.is_active:
-                return (token.user, token)
 
 # TODO: OAuthAuthentication

rest_framework/exceptions.py

@@ -23,6 +23,22 @@ def __init__(self, detail=None):
         self.detail = detail or self.default_detail
 
 
+class AuthenticationFailed(APIException):
+    status_code = status.HTTP_401_UNAUTHORIZED
+    default_detail = 'Incorrect authentication credentials.'
+
+    def __init__(self, detail=None):
+        self.detail = detail or self.default_detail
+
+
+class NotAuthenticated(APIException):
+    status_code = status.HTTP_401_UNAUTHORIZED
+    default_detail = 'Authentication credentials were not provided.'
+
+    def __init__(self, detail=None):
+        self.detail = detail or self.default_detail
+
+
 class PermissionDenied(APIException):
     status_code = status.HTTP_403_FORBIDDEN
     default_detail = 'You do not have permission to perform this action.'