AccessToken extension to the User interface

- `Anything`
  - `Object`
    - `Basic` ...and other supertypes
      - `User`
        - `AccessToken`

- `AccessToken`
  - `User`
    - `Basic`
      - `Identifiable`
      - `Object`
        - `Anything`

no subtypes hierarchy

Initializer
`AccessToken(AccessToken unknown)`

Inherited Attributes
Attributes inherited from: `Object` `hash`, `string`

Methods
`expired` | `shared default Boolean expired()` Check if the access token is expired or not.
`introspect` | `shared default AccessToken introspect(Anything(Throwable?) callback)` Introspect access token. This is an OAuth2 extension that allow to verify if an access token is still valid. Parameters: `callback` The callback function returning the results.
`logout` | `shared default AccessToken logout(Anything(Throwable?) callback)` Revoke refresh token and calls the logout endpoint. This is a openid-connect extension and might not be available on all providers. Parameters: `callback` The callback function returning the results.
`refresh` | `shared default AccessToken refresh(Anything(Throwable?) callback)` Refresh the access token Parameters: `callback` The callback function returning the results.
`revoke` | `shared default AccessToken revoke(String token_type, Anything(Throwable?) callback)` Revoke access or refresh token Parameters: `token_type` A String containing the type of token to revoke. Should be either “access_token” or “refresh_token”. `callback` The callback function returning the results.

Inherited Methods
Methods inherited from: `Object` `equals`
Methods inherited from: `User` `clearCache`, `isAuthorised`, `principal`, `setAuthProvider`