Description of problem:
A customer is experiencing an issue with a NTLM proxy during the ugprade.
As per the strace, the connections through the NTLM proxy with credentials work with subscription-manager/RHSM, and then with yum/urlgrabber,
but NOT with libdnf, the 2nd step used to get the RHEL 8 metadata. This time, we can see in a recvfrom() the proxy returned the error below:
~~~
HTTP/1.1 407 Proxy Authorization Required
Date: Tue, 29 Sep 2020 10:48:59 GMT
Content-Type: text/html
Proxy-Connection: keep-alive
Via: 1.1 COLOIG
Cache-Control: no-store
Content-Language: en
Proxy-Authenticate: Negotiate
Proxy-Authenticate: NTLM
Content-Length: 666
<-cut->
~~~

Version-Release number of selected component (if applicable):
leapp-repository-0.10.0-2.el7_8.noarch
libdnf-0.22.5-1.el7_6.x86_64

How reproducible:
100% for the customer

Actual results:
~~~
2020-09-25 12:56:49.864423 [ERROR] Actor: target_userspace_creator
Message: Unable to install RHEL 8 userspace packages.
Summary:
Details: Command ['systemd-nspawn', '--register=no', '--quiet', '-D', '/var/lib/leapp/scratch/mounts/root_/system_overlay', '--bind=/etc/hosts:/etc/hosts', '--setenv=LEAPP_NO_RHSM=0', '--setenv=LEAPP_EXPERIMENTAL=0', '--setenv=LEAPP_COMMON_TOOLS=:/etc/leapp/repos.d/system_upgrade/el7toel8/tools', '--setenv=LEAPP_COMMON_FILES=:/etc/leapp/repos.d/system_upgrade/el7toel8/files', '--setenv=LEAPP_UNSUPPORTED=0', '--setenv=LEAPP_EXECUTION_ID=6f21afac-8567-4169-bbd9-f230750dcec3', '--setenv=LEAPP_HOSTNAME=XXXXXXXXXXXXXXXXXXX', 'dnf', 'install', '-y', '--nogpgcheck', '--setopt=module_platform_id=platform:el8', '--setopt=keepcache=1', '--releasever', u'8.2', '--installroot', '/el8target', '--disablerepo', '*', '--enablerepo', u'rhel-8-for-x86_64-baseos-rpms', '--enablerepo', u'rhel-8-for-x86_64-appstream-rpms', '--enablerepo', u'rhel-8-for-x86_64-baseos-rpms', '--enablerepo', u'rhel-8-for-x86_64-appstream-rpms', '--enablerepo', u'rhel-8-for-x86_64-appstream-rpms', '--enablerepo', u'rhel-8-for-x86_64-baseos-rpms', 'dnf'] failed with exit code 1.
Stderr: Failed to create directory /var/lib/leapp/scratch/mounts/root_/system_overlay//sys/fs/selinux: Read-only file system
Failed to create directory /var/lib/leapp/scratch/mounts/root_/system_overlay//sys/fs/selinux: Read-only file system
Host and machine ids are equal (96b3ebe3b3db4df38171b3cc3b35a3f4): refusing to link journals
Failed to synchronize cache for repo 'rhel-8-for-x86_64-appstream-rpms', ignoring this repo.
Failed to synchronize cache for repo 'rhel-8-for-x86_64-baseos-rpms', ignoring this repo.
Error: Unable to find a match: dnf
~~~

Additional info:
Sounds close to this kind of bug, fixed in Fedora 26:
https://bugzilla.redhat.com/show_bug.cgi?id=1387622

Suggested the following workaround (still waiting for the feedback as I can't reproduce myself):
~~~

1. echo proxy_auth_method=ntlm > /etc/dnf/dnf.conf
   ~~~