Base Generic View `_allowed_methods` could accept request args.

[Keryn Knight <django@…>]

Currently, ​View._allowed_methods doesn't take into account the potential need for the request to change the availability/discover of methods, if for example the request comes with a token, cookie or whatever that grants additional method access.

_allowed_methods is used in the base View by the ​options HTTP verb and ​in http_method_not_allowed, both of which could pass on request, *args, **kwargs to _allowed_methods, and looking at ​GitHub's results seems to indicate that's the only place it's used. Meanwhile ​Sourcegraph suggests that the only real public usage (admittedly in a largely depended upon package) downstream is in ​Django-Rest-Framework.

[Tim Graham]

We'd probably want to make it a public method as well.

[Tom Christie]

I'm going to recommend that we don't treat _allowed_methods as an overridable bit of public API, or allow for the use case of dynamically altering the results for the Allow header.
The Allow header doesn't necessarily need to reflect which methods are actually permitted, just which are valid.

In REST framework the only thing we do with _allowed_methods is promote it to public, read-only API.