Using a clientId should no longer be forcing token auth in the 1.1 spec

[SimonWoolf]

cf ably/docs#345

┆Issue is synchronized with this Jira Bug by Unito

[SimonWoolf]

@QuintinWillison if and when we get ably-php development going again could we please prioritise this, since we now enforce serverside that 'require-identified' in namespace settings applies to everyone equally, including rest requests made with api keys etc