kwargs to ``BrowserIDBackend.authenticate`` get passed as ``extra_params``

[Osmose]

Any keyword arguments to BrowserIDBackend.authenticate are passed to verify as extra parameters. This might expose data that shouldn't be exposed, though. Instead, it'd be better to add an optional browserid_extra kwarg to authenticate that is passed to verify instead.

[Osmose]

To clarify, we want to add the browserid_extra kwarg to authenticate and we want to stop passing the keyword arguments from authenticate to verify and use the browserid_extra kwarg instead.

[Osmose]

Fixed in bc284f7502fcd91cd9b102deb2b0c7407997b8f4.