A rebuilt version of AltServer for macOS that fixes a critical Apple ID sign-in bug causing app installation/refresh in AltStore to fail with:
NSCocoaErrorDomain 3840, "Encountered unknown tag html"
AppleDeveloperError 3020, "Failed to perform authentication handshake"
Apple.APIError -80009, "MID is invalid"
What's fixed
User-Agent. The outdated string akd/1.0 CFNetwork/978.0.7 Darwin/18.7.0 caused Apple's servers to drop the connection after the 2nd of 3 requests required for sign-in. Replaced with a current AuthKit User-Agent. Based on rileytestut/AltSign#47.
Connection reuse (503 errors). Sign-in now opens a fresh connection on each retry instead of reusing one pinned to a failing Apple backend node. Based on rileytestut/AltSign#49.
anisette machineID on macOS 27 beta. The private AOSKit framework returns empty data on macOS 27, so a runtime patch now routes anisette generation through the public anisette V3 protocol instead. Based on kimziro/altserver-macos27-anisette-fix.
Before installing
Delete your old AltServer config first: remove the folder at ~/Library/Application Support/AltServer before installing this build. Leftover config/cache from a previous install can cause it to behave like the broken official version even after replacing the app.
Installing AltServer
Download and unzip AltServer-macOS27-build.app.zip.
Right click AltServer-macOS27-build.app and choose Open (a normal double click will get blocked by Gatekeeper since this build isn't signed by Apple).
If it's blocked, go to System Settings, then Privacy & Security, and click Open Anyway.
That's it, it works just like the official AltServer.
Getting AltStore itself working on iOS too
The fixes above only patch the macOS side. AltStore's iOS app has the same bug baked into its own sign-in screen, so you'll need one more step:
Install the patched AltServer above first.
Download AltStore-patched.ipa
Open AltServer's menu bar icon, hold Option, and pick AltStore-patched.ipa to install it on your iPhone in place of the regular one.
Notes
This is an unofficial, unsigned build, so use it at your own risk. It's built from rileytestut/AltServer source, combining community fixes from open PRs that haven't been merged upstream yet. It doesn't collect or send any personal data beyond what AltServer normally sends to Apple during sign-in and signing, same as the official release.
Credits
Fixes based on work by BreezeDelegate, Calvin-Zikakis, legeling, and kimziro. Big thanks also to powenn for working out the direct User-Agent patch that fixes AltStore itself on iOS.