Django RestFramework JWT Token: Get User DoesNotExist error - django

Question

After a user is deleted, the tokens on the client side are still valid until the time has expired. The issue is django restframwework does not handle a request from a deleted user and causes a 500. How can I prevent this?
aceback (most recent call last):
File "/lib/python3.6/site-packages/django/core/handlers/exception.py", line 47, in inner
response = get_response(request)
File "/lib/python3.6/site-packages/django/core/handlers/base.py", line 179, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/lib/python3.6/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "/lib/python3.6/site-packages/django/views/generic/base.py", line 70, in view
return self.dispatch(request, *args, **kwargs)
File "/lib/python3.6/site-packages/rest_framework/views.py", line 505, in dispatch
response = self.handle_exception(exc)
File "/lib/python3.6/site-packages/rest_framework/views.py", line 465, in handle_exception
self.raise_uncaught_exception(exc)
File "/lib/python3.6/site-packages/rest_framework/views.py", line 476, in raise_uncaught_exception
raise exc
File "/lib/python3.6/site-packages/rest_framework/views.py", line 493, in dispatch
self.initial(request, *args, **kwargs)
File "/lib/python3.6/site-packages/rest_framework/views.py", line 410, in initial
self.perform_authentication(request)
File "/lib/python3.6/site-packages/rest_framework/views.py", line 324, in perform_authentication
request.user
File "/lib/python3.6/site-packages/rest_framework/request.py", line 220, in user
self._authenticate()
File "/lib/python3.6/site-packages/rest_framework/request.py", line 373, in _authenticate
user_auth_tuple = authenticator.authenticate(self)
File "/lib/python3.6/site-packages/rest_framework_jwt/authentication.py", line 33, in authenticate
payload = jwt_decode_handler(jwt_value)
File "/lib/python3.6/site-packages/rest_framework_jwt/utils.py", line 105, in jwt_decode_handler
secret_key = jwt_get_secret_key(unverified_payload)
File "/lib/python3.6/site-packages/rest_framework_jwt/utils.py", line 26, in jwt_get_secret_key
user = User.objects.get(pk=payload.get('user_id'))
File "/lib/python3.6/site-packages/django/db/models/manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "/lib/python3.6/site-packages/django/db/models/query.py", line 431, in get
self.model._meta.object_name

Answer 1

From the JWT token, you are decoding it to get the user_id - payload['user_id'].
The error is happening because of User.objects.get(pk=payload.get('user_id')).
Instead of doing a get, you could use a get_object_or_404. Use it like so:
from django.shortcuts import get_object_or_404
payload = jwt_decode_handler(jwt_value)
user = get_object_or_404 (User, pk=payload.get('user_id'))
This raises a 404 error when a user will not be found; and that will be bubbled up through your view and handlers to return a 404 statuscode.

Answer 2

The suggestion by Druhn Bala works but would return a 404 error which isn't ideal for my use case. Instead I came up with one that returns a custom response. ValidationError
from rest_framework.exceptions allows you to send a 400 error with a custom response.
def jwt_decode_handler(token):
options = {
'verify_exp': api_settings.JWT_VERIFY_EXPIRATION,
}
# get user from token, BEFORE verification, to get user secret key
try:
unverified_user = jwt.decode(token, None, False)
except User.DoesNotExist:
raise ValidationError({"errors": ['Oops! Something went wrong, please logout and login back in!']})
secret_key = unverified_user.securitysettings.jwt_secret #my custom way of storing a unique jwt uuid per user.
return jwt.decode(
token,
api_settings.JWT_PUBLIC_KEY or secret_key,
api_settings.JWT_VERIFY,
options=options,
leeway=api_settings.JWT_LEEWAY,
audience=api_settings.JWT_AUDIENCE,
issuer=api_settings.JWT_ISSUER,
algorithms=[api_settings.JWT_ALGORITHM]
)
Lastly we set the custom decode handler as the default in settings.py.
JWT_AUTH = {
'JWT_DECODE_HANDLER':
'registration.decoder.jwt_decode_handler',
...
}