title: How to modify the id field in django-rest-framework-simplejwt?
body: <p>I have a custom token serializer:</p>
  <pre><code>from rest_framework_simplejwt.serializers import TokenObtainPairSerializer
  
  class TokenObtainPairWithoutPasswordSerializer(TokenObtainPairSerializer):
  
      def __init__(self, *args, **kwargs):
          super().__init__(*args, **kwargs)
          self.fields['password'].required = False
  
      def validate(self, attrs):
          attrs.update({'password': ''})
          return super(TokenObtainPairWithoutPasswordSerializer, self).validate(attrs)
  </code></pre>
  <p>This worked but now I'd like to change the <code>id</code> -field of my User to be <code>userId</code> and after that I can't get tokens anymore because it is searching for a field <code>id</code>. There must be some pretty simple way to modify this?</p>