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Add support for multiple authentication challenges in WWW-Authenticate header #9242

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Add support for multiple authentication challenges in WWW-Authenticate header #9242

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1cd663c
Add a setting to control WWW-Authenticate header behavior
waxlamp Jan 26, 2024
0a53bb0
Implement alternative WWW-Authenticate generation behaviors
waxlamp Jan 26, 2024
8c23de2
Add documentation for new setting and behavior
waxlamp Jan 26, 2024
525979e
Add a system check for WWW_AUTHENTICATE_BEHAVIOR setting
waxlamp Jan 29, 2024
ea612e2
Fix isort error
waxlamp Jan 29, 2024
146e732
Merge branch 'main' into multiple-www-authenticate
auvipy Apr 2, 2026
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2 changes: 1 addition & 1 deletion docs/api-guide/authentication.md
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Expand Up @@ -79,7 +79,7 @@ When an unauthenticated request is denied permission there are two different err
* [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.
HTTP 401 responses must always include a `WWW-Authenticate` header, that instructs the client how to authenticate. The `www_authenticate_behavior` setting controls how the header is generated: if set to `'first'` (the default), then only the text for the first scheme in the list will be used; if set to `'all'`, then a comma-separated list of the text for all the schemes will be used (see [MDN WWW-Authenticate](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate) for more details). HTTP 403 responses do not include the `WWW-Authenticate` header.
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@peterthomassen peterthomassen Apr 28, 2025

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Setting name should be uppercase

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This paragraph refers to a www_authenticate_behavior setting, but the documented/global setting name added in this PR is WWW_AUTHENTICATE_BEHAVIOR (and the per-view attribute is www_authenticate_behavior). Please rename here to avoid pointing users to a non-existent REST_FRAMEWORK key.

Suggested change
HTTP 401 responses must always include a `WWW-Authenticate` header, that instructs the client how to authenticate. The `www_authenticate_behavior` setting controls how the header is generated: if set to `'first'` (the default), then only the text for the first scheme in the list will be used; if set to `'all'`, then a comma-separated list of the text for all the schemes will be used (see [MDN WWW-Authenticate](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate) for more details). HTTP 403 responses do not include the `WWW-Authenticate` header.
HTTP 401 responses must always include a `WWW-Authenticate` header, that instructs the client how to authenticate. The `WWW_AUTHENTICATE_BEHAVIOR` setting controls how the header is generated: if set to `'first'` (the default), then only the text for the first scheme in the list will be used; if set to `'all'`, then a comma-separated list of the text for all the schemes will be used (see [MDN WWW-Authenticate](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate) for more details). HTTP 403 responses do not include the `WWW-Authenticate` header.

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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**.
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With WWW_AUTHENTICATE_BEHAVIOR='all', the 401 vs 403 decision is no longer determined solely by the first authentication class (any authenticator that returns a challenge will keep the response as 401). Please update/qualify this sentence so it remains accurate under the new setting.

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7 changes: 7 additions & 0 deletions docs/api-guide/settings.md
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Expand Up @@ -189,6 +189,13 @@ The class that should be used to initialize `request.auth` for unauthenticated r

Default: `None`

#### WWW_AUTHENTICATE_BEHAVIOR

Determines whether a single or multiple challenges are presented in the `WWW-Authenticate` header.

This should be set to `'first'` (the default value) or `'all'`. When set to `'first'`, the `WWW-Authenticate` header will be set to an appropriate challenge for the first authentication scheme in the list.
When set to `'all'`, a comma-separated list of the challenge for all specified authentication schemes will be used instead (following the [syntax specification](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate)).
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@peterthomassen peterthomassen Apr 28, 2025

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RFC 9110 also warns:

Some user agents do not recognize this form, however. As a result, sending a WWW-Authenticate field value with more than one member on the same field line might not be interoperable.

Perhaps we should have a similar warning somewhere, either here or in authentication.md.

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Grammar: “a comma-separated list of the challenge for all specified authentication schemes” should be “...list of the challenges...” (plural).

Suggested change
When set to `'all'`, a comma-separated list of the challenge for all specified authentication schemes will be used instead (following the [syntax specification](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate)).
When set to `'all'`, a comma-separated list of the challenges for all specified authentication schemes will be used instead (following the [syntax specification](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/WWW-Authenticate)).

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---

### Test settings
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1 change: 1 addition & 0 deletions rest_framework/apps.py
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Expand Up @@ -8,3 +8,4 @@ class RestFrameworkConfig(AppConfig):
def ready(self):
# Add System checks
from .checks import pagination_system_check # NOQA
from .checks import www_authenticate_behavior_setting_check # NOQA
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@waxlamp waxlamp Jan 29, 2024

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Is this line necessary? In my local build I was able to trigger the new error without it; I merely copied the pattern from the line above in my PR.

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@peterthomassen peterthomassen Apr 28, 2025

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Good question; have you been able to understand this further?

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@peterthomassen peterthomassen Apr 28, 2025

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This is following this advice from the Django docs:

Checks should be registered in a file that’s loaded when your application is loaded; for example, in the AppConfig.ready() method.

When you say you were able to trigger the new error without this: did this happen on startup, or when you ran check manually?

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@waxlamp waxlamp Jun 13, 2025

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I think I understand this better now.

The @register decorator causes the check function to be registered; all that's required beyond using the decorator is to arrange to load the module in which those functions live. That's why omitting this line still allows my check to be performed (on both startup, and when invoking the check management command manually, as it happens): the previous line causes the whole module to load, which causes not just pagination_system_check but my new check function to be registered as well.

I tested this theory by removing both lines; in that case, my check does not run. But this means that both lines can be replaced with just from . import checks; that's sufficient to register all the check functions in that module.

I hope all this made sense 🙂. If it does, I'll plan to make that change and resolve this conversation.

21 changes: 20 additions & 1 deletion rest_framework/checks.py
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@@ -1,4 +1,4 @@
from django.core.checks import Tags, Warning, register
from django.core.checks import Error, Tags, Warning, register


@register(Tags.compatibility)
Expand All @@ -19,3 +19,22 @@ def pagination_system_check(app_configs, **kwargs):
)
)
return errors


@register(Tags.compatibility)
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@peterthomassen peterthomassen Apr 28, 2025 •
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This probably should be Tags.security, see for example all the checks in https://github.com/django/django/blob/0ee06c04e0256094270db3ffe8b5dafa6a8457a3/django/core/checks/security/base.py

Those checks also use deploy=True, which causes them to only run with check --deploy. Not sure is this is a good idea. OTOH, it's done the same way for all the other validity checks for security settings.

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@waxlamp waxlamp Jun 13, 2025

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I went with Tags.compatibility largely because the other existing check is also looking to validate settings (which is all my check does, really). Tags.security seems to have more to do with actual security checks (rather than mere misconfiguration). Apparently it is also possible to omit the tag entirely.

I'm happy to go with any of these options, just let me know what you prefer.

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@peterthomassen peterthomassen Jun 16, 2025

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Sure, I have no strong preference.

def www_authenticate_behavior_setting_check(app_configs, **kwargs):
errors = []
# WWW_AUTHENTICATE_BEHAVIOR setting must be 'first' or 'all'
from rest_framework.settings import api_settings
setting = api_settings.WWW_AUTHENTICATE_BEHAVIOR
if setting not in ['first', 'all']:
errors.append(
Error(
"The rest_framework setting WWW_AUTHENTICATE_BEHAVIOR must be either "
f"'first' or 'all' (it is currently set to '{setting}').",
hint="Set WWW_AUTHENTICATE_BEHAVIOR to either 'first' or 'all', "
"or leave it unset (the default value is 'first').",
id="rest_framework.E001",
)
)
return errors
1 change: 1 addition & 0 deletions rest_framework/settings.py
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Expand Up @@ -78,6 +78,7 @@
# Authentication
'UNAUTHENTICATED_USER': 'django.contrib.auth.models.AnonymousUser',
'UNAUTHENTICATED_TOKEN': None,
'WWW_AUTHENTICATE_BEHAVIOR': 'first',
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Why isn't this a boolean, e.g. WWW_AUTHENTICATE_ALL = False (by default)?

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@waxlamp waxlamp Jun 13, 2025

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I suppose I was leaving the door open for other modes beyond 'first' and 'all', but I think a boolean setting makes more sense here.


# View configuration
'VIEW_NAME_FUNCTION': 'rest_framework.views.get_view_name',
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8 changes: 7 additions & 1 deletion rest_framework/views.py
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Expand Up @@ -108,6 +108,7 @@ class APIView(View):
renderer_classes = api_settings.DEFAULT_RENDERER_CLASSES
parser_classes = api_settings.DEFAULT_PARSER_CLASSES
authentication_classes = api_settings.DEFAULT_AUTHENTICATION_CLASSES
www_authenticate_behavior = api_settings.WWW_AUTHENTICATE_BEHAVIOR
throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
Expand Down Expand Up @@ -192,8 +193,13 @@ def get_authenticate_header(self, request):
header to use for 401 responses, if any.
"""
authenticators = self.get_authenticators()
www_authenticate_behavior = self.www_authenticate_behavior
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get_authenticate_header() silently returns None for any www_authenticate_behavior value other than 'first'/'all', which will coerce NotAuthenticated into a 403. Since www_authenticate_behavior can be overridden per-view (bypassing the system check), consider adding an explicit fallback (eg default to 'first') or raising a clear configuration error so misconfiguration doesn’t change response semantics silently.

Suggested change
www_authenticate_behavior = self.www_authenticate_behavior
www_authenticate_behavior = self.www_authenticate_behavior
# Ensure that misconfiguration of `www_authenticate_behavior` does not
# silently change response semantics. Fall back to the default
# behavior of using the first authenticator if an unexpected value
# is provided at the view level.
if www_authenticate_behavior not in ('first', 'all'):
www_authenticate_behavior = 'first'

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if authenticators:
return authenticators[0].authenticate_header(request)
if www_authenticate_behavior == 'first':
return authenticators[0].authenticate_header(request)
elif www_authenticate_behavior == 'all':
challenges = (a.authenticate_header(request) for a in authenticators)
return ', '.join((c for c in challenges if c is not None))

def get_parser_context(self, http_request):
"""
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