Add doc section for auth media

[devonh]

No description provided.

[anoadragon453]

A few things here and there, but overall on track!

[anoadragon453]

LGTM! Just a couple tiny suggestions below.

[anoadragon453]

Suggested change

	will responde with a `MCS_MEDIA_REQUEST_FAILED`.
	will respond with HTTP status 502, errcode `MCS_MEDIA_REQUEST_FAILED`.

ref:

matrix-content-scanner-python/src/matrix_content_scanner/scanner/file_downloader.py

Lines 210 to 231 in 694914f

	# If the response isn't a 200 OK, raise.
	if 200 < code:
	logger.info("Response body: %s", body)
	# If the response is a 404 or an "unrecognised request" à la Synapse,
	# consider that we could not find the media, and that we should retry if this
	# request was directed at a v3 endpoint.
	if code == 400:
	try:
	err = json.loads(body)
	if err["errcode"] == "M_UNRECOGNIZED":
	raise _PathNotFoundException
	except (json.decoder.JSONDecodeError, KeyError):
	pass
	if code == 404:
	raise _PathNotFoundException
	raise ContentScannerRestError(
	HTTPStatus.BAD_GATEWAY,
	ErrCode.REQUEST_FAILED,
	"The remote server responded with an error",
	)

Seems like we should probably be returning a 401 here though, in line with other Matrix-esque endpoints? (This doesn't need to be fixed here, but if you agree then we can track this in a separate issue.)

[devonh]

Yup yup - this should be changed to be more helpful for clients to understand what is going wrong.
Issue: #72