ureq http_client doesn't work with microsoft (tested for devicecode flow)

[nerditation]

I was trying to authenticate using microsoft devicecode flow, as documented here, but the server returned 404. but I got a totally normal response when I directly post the authentication data to the endpoint using ureq::Request::send_form(...)

so I checked the logs and found that there were different http headers: the failed on has a Transfer-Encoding: chunked header, while the good one contains a Content-Length: 12345678 header.

I don't know whether microsoft's implementation is correct, or what the oauth standard says, but I found the reason leading to this difference is oauth2::ureq::http_client calls send(reader) on the ureq::Request object:

oauth2-rs/src/ureq.rs

Line 55 in 93452e5

req.send(&*request.body)

but we could instead (and should) call send_bytes(byte_slice) since the body is already serialized data (urlencoded form), why add another indirection to wrap it into a reader?

    req.send_bytes(&request.body)

this not only feels more nature, it also fixes the compatibility issue with microsoft since payload with type of slice makes ureq automatically add a Content-Length header.

[ramosbugs]

Sounds like a good fix. Please feel free to submit a PR!