Create a user and token, given an email. If user exists just
        provide the token.

def post(self, request):
        '''Create a user and token, given an email. If user exists just
        provide the token.'''
        serializer = CreateUserSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)

        email = serializer.validated_data.get('email')
        try:
            user = User.objects.get(username=email)
        except User.DoesNotExist:
            user = User.objects.create_user(email, email=email)
        token, created = Token.objects.get_or_create(user=user)

        return Response(
            status=status.HTTP_201_CREATED, data={'token': token.key})