Why do I get "Warning: Repository 'oss_update' appears to be outdated. Consider using a different mirror or server."?

I found the answer from https://www.reddit.com/r/bashonubuntuonwindows/comments/8fcbs5/update_of_opensuse_on_wsl_error/ : you need to change the repository URIs from HTTP to HTTPS. I just did that and was able to see new packages. I only had the oss and oss_update repositories, so the process I followed was:

sudo zypper rr oss
sudo zypper rr oss_update
sudo zypper ar https://download.opensuse.org/distribution/leap/42.3/repo/oss/suse/ oss
sudo zypper ar https://download.opensuse.org/update/leap/42.3/oss/ oss_update

sudo zypper ref
sudo zypper up

To make sure this works for your version, find the version number of your system, and substitute it into the above URLs in the place of 42.3. (You can make sure the URLs are valid by opening them in a browser.) You can see the version number in the output of the following command:

cat /etc/os-release

For Leap 15.0 remove (suse/ from distribution link):

sudo zypper rr oss
sudo zypper rr oss_update

sudo zypper ar https://download.opensuse.org/distribution/leap/15.0/repo/oss/ oss
sudo zypper ar https://download.opensuse.org/update/leap/15.0/oss/ oss_update

sudo zypper ref
sudo zypper up