title: rest_framework.authtoken refresh on change password
body: <p>I have successfully(hopefully) managed to implement a change_password action.</p>
  
  <p>However, after I change the password, the client automatically logsout. (token is probably not valid anymore)</p>
  
  <p>I would like the API Client to remain logged in after a password reset to make other requests with the new token.</p>
  
  <p>Is there an equivalent for <strong>update_session_auth_hash(request, self.object)</strong> ?</p>
  
  <p>Serializers:</p>
  
  <pre><code>class PasswordSerializer(serializers.Serializer):
      """
      Serializer for password change endpoint.
      """
      old_password = serializers.CharField(required=True)
      new_password = serializers.CharField(required=True)
  </code></pre>
  
  <p>API View</p>
  
  <pre><code>    @action(methods=['put'], detail=True)
      def change_password(self, request, pk):
          serializer = PasswordSerializer(data=request.data)
          if serializer.is_valid():
              user = get_object_or_404(User, pk=pk)
              if user != request.user:
                  return Response({'error': "Cannot change other user's password"},
                                  status=status.HTTP_403_FORBIDDEN)
              else:
                  if not user.check_password(serializer.data.get('old_password')):
                      return Response({'old_password': ['Wrong password.']},
                                      status=status.HTTP_400_BAD_REQUEST)
                  user.set_password(request.POST.get('new_password'))
                  user.save()
          else:
              return Response(serializer.errors,
                              status=status.HTTP_400_BAD_REQUEST)
          return Response({'details': 'Success'}, status=status.HTTP_200_OK)
  </code></pre>