class UserAuthenticationView(APIView):
    def post(self, request, *args, **kwargs):
        serializer = UserAuthenticationSerializer(data=self.request.data)
        if serializer.is_valid():
            user = serializer.validated_data['user']
            return Response({'token': user.auth_token.key}, status=status.HTTP_200_OK)

        return Response(serializer.errors, status=status.HTTP_401_UNAUTHORIZED)

class UserAuthenticationSerializer(serializers.Serializer):
    username = serializers.CharField()
    password = serializers.CharField()

    def validate(self, attrs):
        username = attrs.get('username')
        password = attrs.get('password')

        if username and password:
            user = authenticate(username=username, password=password)
            if user:

                if not user.is_active:
                    msg = 'User account is disabled.'
                    raise serializers.ValidationError(msg, code='authorization')

            else:
                msg = 'Unable to log in with provided credentials.'
                raise serializers.ValidationError(msg, code='authorization')

        else:
            msg = 'Must include "username" and "password".'
            raise serializers.ValidationError(msg, code='authorization')

        attrs['user'] = user
        return attrs