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.
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.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].
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.
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.
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.
If you are deploying to Apache, and using any non-session based authentication, you will need to explicitly configure mod_wsgi to pass the required headers through to the application. This can be done by specifying the `WSGIPassAuthorization` directive in the appropriate context and setting it to `'On'`.
This authentication scheme uses [HTTP Basic Authentication][basicauth], signed against a user's username and password. Basic authentication is generally only appropriate for testing.
Unauthenticated responses that are denied permission will result in an `HTTP 401 Unauthorized` response with an appropriate WWW-Authenticate header. For example:
**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.
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.
For clients to authenticate, the token key should be included in the `Authorization` HTTP header. The key should be prefixed by the string literal "Token", with whitespace separating the two strings. For example:
Unauthenticated responses that are denied permission will result in an `HTTP 401 Unauthorized` response with an appropriate WWW-Authenticate header. For example:
Note that the default `obtain_auth_token` view explicitly uses JSON requests and responses, rather than using default renderer and parser classes in your settings. If you need a customized version of the `obtain_auth_token` view, you can do so by overriding the `ObtainAuthToken` view class, and using that in your url conf instead.
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 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`, `PATCH`, `POST` or `DELETE` requests. See the [Django CSRF documentation][csrf-ajax] for more details.
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.
* 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 `.authenticate_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 `.authenticate_header()` method is not overridden, the authentication scheme will return `HTTP 403 Forbidden` responses when an unauthenticated request is denied access.
The following third party packages are also available.
## Digest Authentication
HTTP digest authentication is a widely implemented scheme that was intended to replace HTTP basic authentication, and which provides a simple encrypted authentication mechanism. [Juan Riaza][juanriaza] maintains the [djangorestframework-digestauth][djangorestframework-digestauth] package which provides HTTP digest authentication support for REST framework.
