fix(auth): append trailing slash to native/fast authenticate endpoint

[Vadim-B52]

Apple's account bag now returns the authentication endpoint as https://auth.itunes.apple.com/auth/v1/native/fast. That endpoint only responds correctly when the path has a trailing slash; posting to it without the slash makes Apple's edge return a 301/204 with an empty or HTML body, so 'ipatool auth login' fails to parse the response and silently dies (observed as the 'plist: unexpected hex digit' error or a -5000 with no usable message).

ipatool posted the endpoint verbatim as received from the bag. Add authenticateURL() to normalize /native/ endpoints by appending the trailing slash (legacy MZFinance endpoint left untouched), and use it in loginRequest.

Also improve http client diagnostics: when an XML response body is not a property list, return 'unexpected response from Apple (HTTP ): ' instead of the opaque plist parse error.

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Summary by cubic

Fix login failures against Apple’s native auth endpoint by appending a trailing slash. Also make XML error responses readable when Apple returns HTML instead of a plist.

• Bug Fixes
  • Normalize /native/ auth endpoints via authenticateURL() to append a trailing slash; used in loginRequest and leaves legacy MZFinance endpoints unchanged.
  • Improve pkg/http XML handling: when the body isn’t a plist, return unexpected response from Apple (HTTP <code>): <snippet> with HTML stripped, avoiding the opaque “plist: unexpected hex digit” error.

^{Written for commit a69db1ab97731d50037c1cfaf9152ca75119d60d. Summary will update on new commits.}

[jpstotz]

I think we already have quite a few PRs on that topic. It would be nice if you could describe your changes compared to the other PRs like #505 #502 #493 ...

[tap3w0rm]

Confirmed this fixes the auth login failure on Windows.

Environment:

• Windows
• ipatool v2.3.0 release failed with:
  failed to unmarshal xml: plist: error parsing text property list: unexpected hex digit h``
• Built this PR branch at a69db1a
• Login completed successfully with the patched build
• Successfully downloaded an App Store IPA afterward

Thanks for the fix.