Something broke in refactoring of url instantiation (#3364)

[fredriklj]

After some users upgraded to httpx version >= 0.28.0 they could no longer authenticate through the oauth2 flow. The issue is described here:

CJNE/pyporscheconnectapi#66

After going through the diff between 0.27.2 and 0.28.0 I isolated the problem to be the #3364 PR. If I revert the following lines of code, it all starts working again:

--- a/httpx/_models.py
+++ b/httpx/_models.py
@@ -396,7 +396,9 @@ class Request:
         extensions: RequestExtensions | None = None,
     ) -> None:
         self.method = method.upper()
-        self.url = URL(url) if params is None else URL(url, params=params)
+        self.url = URL(url)
+        if params is not None:
+            self.url = self.url.copy_merge_params(params=params)
         self.headers = Headers(headers)
         self.extensions = {} if extensions is None else dict(extensions)

I have not had the opportunity to verify what exactly the effect of the change is on the wire, but I have verified that this change is the cause of the problems, and that reverting it resolves the matter.

[fredriklj]

Ok, looking at it further I see there are active discussions already ongoing around this:

#3433
#3428

Guidance would be much appreciated if this is really the intended behaviour of this change, and if we should merge the parameters ourselves instead of relying on httpx to do the job?