How to work with Custom Claims

Hey, I’m looking for the best approach to apply okta into my workflow.
Currently I’m using Auth service based on net core and IdentityServer4 for authentication. I’m storing list of clients in db, each client consists of ClientId,Secret,Name,Claims(array of string). To get JWT token, customer have to do request to the auth service using ClientId and Secret, if it’s valid then service returns a JWT token with my custom claims that was assigned to the client.

I would like to have similar approach in OKTA, what would be the best option to do that?
What I’ve tried:
-Create Custom Profile in Users panel, that contains Claims field, then create new user based on this profile
-Assign user to the application(web type because service type seems doesn’t work?)
-Add new claim to the Authorization Server
-Token preview shows that token contains my custom claims

I was able to make it works only with Implicit grant type, is it possible to make it work for client-credentials?
Currently I have about 1000 users in my system, so in this case I have to create 1000 application and 1000 users with profile in OKTA, right?
I see it’s working in the Token preview tab, but how should postman request look(what endpoint I should hit, how add user to the request-don’t see any userId)?
Do you know better way to handle my workflow?

Can anyone advise?

@dmen93 Please refer the answer in this dev discussion for the same question