Git source HTTP clients previously disabled redirects entirely, so API
calls for renamed repositories (e.g. GitHub 301 to /repositories/{id})
failed. Add SafeExternalUrl::sameOriginRedirectOptions() and use it in
the GitSource HTTP macro to follow up to five strict redirects that stay
on the same scheme, host and port.
A redirect to a different origin gets a RequestException, because the
DNS pin covers only the original host and port. This blocks SSRF via
redirects to metadata or attacker hosts. Authorization headers and the
original request method and body are kept on same-origin redirects.
Tests cover following same-host redirects, keeping POST on a redirect,
refusing cross-host/scheme/port redirects and the five-redirect cap.
Andras Bacsai