Hello!
There are 2 ways to achieve what you want.
First is to import your existing keys to Tyk, this is not really documented, but you can “import” key with your ID using Gateway API like this: `POST /tyk/keys/ with key data as body (for the key data see https://tyk.io/docs/get-started/with-tyk-hybrid/tutorials/create-api-token/)
Another option will be using middleware, and define “pre” middleware, which do the token mapping, by querying some service/kv storage provided by you.
Hope it makes sense!
Leon, Tyk Team