AltServer (macOS 27 fix) working Apple ID sign-in for AltStore

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 The outdated string akd/1.0 CFNetwork/978.0.7 Darwin/18.7.0 caused Apple's servers to drop the connection after the 2nd of 3 requests required for sign-in.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.

⚠️ THE "INSTALL ALTSTORE" BUTTON IN ALTSERVER'S MENU DOES NOT WORK, DO NOT USE IT. ⚠️ It pulls the official, unpatched AltStore build and will just give you the same broken sign-in. Use the patched AltStore-patched.ipa below instead (Option-click method).

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.

AltServer Fixed Build (GSA Login + macOS 27 Anisette)

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; a runtime patch now routes anisette generation through the public anisette V3 protocol instead. (based on kimziro/altserver-macos27-anisette-fix)

Installation
Download and unzip AltServer.zip.
Right-click AltServer.app → Open (a normal double-click will be blocked by Gatekeeper, since this build isn't signed by Apple).
If blocked, go to System Settings → Privacy & Security → Open Anyway.
Done - works just like the official AltServer.
Notes
This is an unofficial, unsigned build - use at your own risk.
Architecture: x86_64 (runs via Rosetta on Apple Silicon; macOS will prompt to install Rosetta on first launch if it isn't already installed).
Built from rileytestut/AltServer source, combining community fixes from open PRs not yet merged upstream.
This build does not collect or transmit any personal data beyond AltServer's normal communication with Apple's servers (identical to the official release).

Credits

Fixes based on work by BreezeDelegate, Calvin-Zikakis, legeling, and kimziro.

I used this to install the IPA files I needed onto my iPhone - forgot to mention that this only fixes the macOS side; on iOS you'll still get that same error. But AltServer has a feature to sideload IPA files directly without going through AltStore on iOS - you download the IPA file on your Mac, hold Option in the open AltServer menu, and select the IPA file you want to install.