Support access-control-max-age header

[simonw]

This header allows the client to remember the CORS result so it doesn't have to perform a pre-flight OPTIONS request before every POST etc.

access-control-max-age: 7200

[simonw]

I tested this - and the other features - with a tiny temporary plugin here running on Datasette Cloud: https://gist.github.com/simonw/59ccfeb2a9de09151d08df2b64336d03

from asgi_cors import asgi_cors
from datasette import hookimpl


@hookimpl
def asgi_wrapper(datasette):
    def wrap_with_asgi_cors(app):
        return asgi_cors(
            app,
            allow_all=True,
            methods=("GET", "POST", "OPTIONS"),
            headers=("authorization", "link", "content-type"),
            max_age=60
        )

    return wrap_with_asgi_cors

Here's a screenshot showing the 60s access-control-max-age working: