The initial DISCORD_ALLOWED_ROLES implementation (#11608, merged from #9873)
scans every mutual guild when resolving a user's roles. This allows a
cross-guild DM bypass:
1. Bot is in both public server A and private server B.
2. User holds the allowed role in server A only.
3. User DMs the bot. The role check finds the role in A and authorizes the
DM, granting access as if the user were trusted in server B.
Fix:
- DMs (no guild context) disable role-based auth by default. Opt-in via
DISCORD_DM_ROLE_AUTH_GUILD=<guild_id> restricts role lookup to one
explicitly-trusted guild.
- Guild messages check roles only in the originating guild
(message.guild), never in other mutual guilds.
- Reject cached author.roles when the Member came from a different guild
than the current message.
Backwards compatibility:
- DISCORD_ALLOWED_USERS behavior is unchanged (still works in both DMs
and guild messages).
- Deployments that rely on roles in guild channels continue to work;
role checks are now strictly scoped to that guild.
- Deployments that intentionally want role-based DM auth can opt into a
single trusted guild via DISCORD_DM_ROLE_AUTH_GUILD.
Tests: 9 new regression guards in
tests/gateway/test_discord_roles_dm_scope.py covering the bypass path,
the opt-in path, cross-guild guild-message bypass, and backwards-compat
user-ID paths. 47/47 discord-auth tests pass.
Refs: #11608 (initial implementation), #7871 (feature request),
#9873 (PR author credit @0xyg3n)
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