The lifetime of the access token, in milliseconds. Once
the access token has expired a new access token can be
obtained by using the provided refresh token. If no
refresh token is provided, the client will need to re-log in
to obtain a new access token. If not given, the client can
assume that the access token will not expire.
Optional client configuration provided by the server. If present,
clients SHOULD use the provided object to reconfigure themselves,
optionally validating the URLs within. This object takes the same
form as the one returned from .well-known autodiscovery.