client_auth: Document GSSAPI channel binding and GSSAPI client usage - #1706

On December 2, 2026, GitHub will restrict `pull_request_target` on public repositories by default. To continue allowing the event trigger, configure an Actions policy. Learn more: https://gh.io/securely-using-pull_request_target#default-policy-for-pull_request_target

Line matches candidate pattern (base64 encoded content) ``([`'"])[-a-zA-Z=;:/0-9+]+=\g{-1}`` (candidate-pattern)

Line matches candidate pattern (base64 encoded content) ``([`'"])[-a-zA-Z=;:/0-9+]+=\g{-1}`` (candidate-pattern)

Line matches candidate pattern (base64 encoded content) ``([`'"])[-a-zA-Z=;:/0-9+]+=\g{-1}`` (candidate-pattern)