Fields not appearing for POST api - django Rest Framework

Question

I am trying to write API for SignIn, Register using django Rest framework. I wrote a simple serializer for auth User.

class UserSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = get_user_model()
        fields = ('url', 'username', 'password')

Then in my view

@api_view(['POST'])
def signIn(request):
    serialized = UserSerializer(data=request.DATA)
    if serialized.is_valid():
         // authenticate user

Why my fields(username & password) are not appearing on swagger(django-rest-swagger) or API browsable view ? Any help will be appreciated.