feat(sdk): expose AccessTokenSource

[dschmidt]

Proposed Changes

Expose AccessTokenSource from SDK instance. This would allow me to reuse an existing IDPTokenExchangeTokenSource instance.

Context

I'm retrieving the entitlements for a user while using the ClaimsEntityResolutionService. For that I'm retrieving an EntityChain via client.EntityResoution.CreateEntityChainFromJwt and pass that to client.Authorization.GetEntitlements.

I would like to avoid implementing the token exchange myself when there's already an implementation available through the sdk. Unfortunately it's a bit cumbersome to setup, so I would like to reuse the existing instance from the sdk, which currently is not exposed.

Checklist

• [ ] I have added or updated unit tests
• [ ] I have added or updated integration tests (if appropriate)
• [ ] I have added or updated documentation

Testing Instructions