AddToRole and IdentityRole is not part of the model for the current context

I’m using Identity 2.1 to handle the user roles in my asp.net application. So far so good, i created new context extending from IdentityDBContext, extending the IdentityUser and IdentityRole to add a couple of new fields. However, whenever im trying to add a user to a specific role using the UserManager im getting The entity type IdentityRole is not part of the model for the current context.. So there seem to be something wrong with the user-role relationship, here is my code so far for reference:

check user validation in Asp.net core with jwt authorization

I implemented Microsoft Identity and JWT in my web api,
a client can login and get a JWT token and store it in the application.
since the expiration of the token the user can access the the server,
but if I remove a user from my database, the removed user still has its token and can access the web api,
how can I check the validation of the user?