BF: Properly handle HTTP403 by using internal download helper

Previous request result handling assumed that HTTP error codes
necessarily result in exceptions, which they do not.

Instead of implementing error handling per request, use an existing
abstraction.

Fixes dataladgh-5023

... although it could be made better by supporting git-credentials as
a credential sources in DataLad.

datalad/core/distributed/clone.py

@@ -12,6 +12,7 @@
 import logging
 import re
 import requests
+from tempfile import TemporaryDirectory
 from os.path import expanduser
 from collections import OrderedDict
 from urllib.parse import unquote as urlunquote
@@ -45,6 +46,7 @@
     EnsureStr,
     EnsureKeyChoice,
 )
+from datalad.support.exceptions import DownloadError
 from datalad.support.param import Parameter
 from datalad.support.network import (
     get_local_file_url,
@@ -59,6 +61,7 @@
 )
 from datalad.utils import (
     assure_bool,
+    download_url,
     knows_annex,
     make_tempfile,
     Path,
@@ -630,12 +633,14 @@ def postclonecfg_ria(ds, props):
         scheme = props['giturl'].split(':', 1)[0]
         if scheme in ['http', 'https']:
             try:
-                response = requests.get("{}{}config".format(
-                    props['giturl'],
-                    '/' if not props['giturl'].endswith('/') else '')
-                )
-                config_content = response.text
-            except requests.RequestException as e:
+                with TemporaryDirectory() as _dest:
+                    config_content = open(
+                        download_url(
+                            "{}{}config".format(
+                                props['giturl'],
+                                '/' if not props['giturl'].endswith('/') else ''),
+                            _dest)).read()
+            except DownloadError as e:
                 lgr.debug("Failed to get config file from source:\n%s",
                           exc_str(e))
 
@@ -662,8 +667,8 @@ def postclonecfg_ria(ds, props):
                 lgr.debug("Failed to get config file from source: %s",
                           exc_str(e))
         else:
-            lgr.debug("Unknown URL-Scheme in %s. Can handle SSH, HTTP or "
-                      "FILE scheme URLs.", props['source'])
+            lgr.debug("Unknown URL-Scheme %s in %s. Can handle SSH, HTTP or "
+                      "FILE scheme URLs.", scheme, props['source'])
 
         # 3. And read it
         org_uuid = None