## Summary
Adds `--ai-gateway-allow-byok` deployment option to control whether
users can use Bring Your Own Key (BYOK) mode with AI Gateway.
When disabled (`--ai-gateway-allow-byok=false`), BYOK requests are
rejected with a 403 and a message directing the admin to enable the
flag. Centralized key authentication works regardless of this setting.
Defaults to `true` (BYOK allowed).
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Co-authored-by: Danny Kopping <danny@coder.com>