seeing the same here -- thought I'd bungled my code somehow, but looks like I'm not alone. I've got the "Bad Request" on initial call to calendar https://caldav.iclound.com, with Depth: 0. Worked last week.
Don't you get any other information back from server, as HTTP body in the 400 response ?
May read this:
Where did you get the syntax of this request ?
Is it RFC 4918 ? h ttps://tools.ietf.org/html/rfc4918
I read here an example
and see that
<D:propfind xmlns:D="DAV:"> contains more information to provide an url
Could it be the problem ?
from caldav.icloud.com, no content is returned, only 400 error.
< HTTP/1.1 400 Bad Request < Server: AppleHttpServer/e70a1a237a4f < Date: Fri, 13 Sep 2019 18:05:29 GMT < Content-Length: 0 < Connection: keep-alive
"Bad Request" is typically user-provided bad information, (rather than a permission problem), as it worked last week and not now, I suspect it's a recent change on the server-side.
Same issue applies to https://caldav.icloud.com. I just started noticing today, and someone else brought it up on StackOverflow:
Hoping this gets fixed soon!
There's a temporary solution for the issue, it's hacky but works like charm...