We're attempting to run the DXA 1.7 upgrade script on our CM server. At first glance, this looks like an issue with IIS authentication settings, for the SDL Web site or one of its applications. However, we're tried every different combination we could think of (enabling Anonymous authentication for everything, disabling it, enabling/disabling Windows authentication, comparing our IIS settings to an environment where the upgrade script runs without issue, etc.). We also made sure the DXA .zip file was unblocked before unpacking it, as discussed here.
At this point, we suspect it is something to do with Local Security Settings, or some similar issue as described here. However, unfortunately, our server is pretty locked down, in such a way that we don't have access to make changes to local security settings, and getting access may be very difficult.
I was wondering if anyone has suggestions for what else the issue might be or for an alternative approach to getting the CM updated to DXA 1.7.