[REQ] support user provided authenticator in api client

Created by: zshihang

Is your feature request related to a problem? Please describe.

need an authenticator to refresh bearer token every X minutes in api client

Describe the solution you'd like

the typescript client generator already solved this by allowing user to supply a default authenticator. https://github.com/OpenAPITools/openapi-generator/blob/6dc3216f6d8c8566931552a59198c3e13cfaa291/modules/openapi-generator/src/main/resources/typescript-node/api-single.mustache#L43 we probably need to do the same thing to other generators, e.g. java, python,...etc..