Added OAuth-Based Discord Account Integration (Mirror)

[yulmwu]

• Refs: Added OAuth-Based Discord Account Integration wargame#19

This PR introduces Discord account integration using OAuth. Once a user links their Discord account, they are automatically joined to a designated Discord server and assigned a role.

All Discord interactions are handled by a separate service independent of the main backend. The backend is responsible only for managing OAuth clients and storing account-linking information. The overall flow is shown below.

The following backend environment variables have been added:

# Discord Account Linking (OAuth2 on the backend; bot runs as a separate server)
DISCORD_ENABLED=true
DISCORD_CLIENT_ID=
DISCORD_CLIENT_SECRET=
# redirect_uri = the URL the BROWSER hits at the backend callback. Register it
# verbatim in the Discord Developer Portal (OAuth2 > Redirects; multiple allowed)
# and keep it identical here (scheme/host/port/path all matter).
#   - local direct:  http://localhost:8080/api/discord/callback
#   - production:    https://internal.swua.kr/wargame/api/discord/callback
DISCORD_REDIRECT_URI=http://localhost:8080/api/discord/callback
DISCORD_OAUTH_SCOPES=identify guilds.join
DISCORD_STATE_TTL=5m
DISCORD_OAUTH_TIMEOUT=10s
# Where to send the browser after the OAuth callback (frontend profile page).
#   - production: https://wargame.swua.kr/profile
DISCORD_SUCCESS_REDIRECT=http://localhost:3000/profile
# Invite link shown to users not yet in the guild (fallback button).
DISCORD_INVITE_URL=
# Auto-join the guild via guilds.join scope after linking.
DISCORD_AUTO_JOIN=true
# Connection to the separate Discord bot server.
DISCORD_BOT_BASE_URL=http://localhost:8083
DISCORD_BOT_SECRET=change-me
DISCORD_BOT_TIMEOUT=5s

DISCORD_CLIENT_ID and DISCORD_CLIENT_SECRET can be obtained from the Discord Developer Portal. You must also configure the corresponding Redirect URI.

In addition, DISCORD_BOT_SECRET must match the value used by the Invite Bot/Server. The following environment variables have been added for the Invite Bot/Server:

# Discord bot server configuration.
# The bot owns all Discord secrets; the wargame backend never sees these.

# HTTP server (internal API consumed by the wargame backend)
HTTP_ADDR=:8083

# Shared secret — MUST equal DISCORD_BOT_SECRET in the wargame backend .env
DISCORD_INTERNAL_SECRET=change-me

# Discord application / bot
DISCORD_BOT_TOKEN=
DISCORD_GUILD_ID=
DISCORD_VERIFIED_ROLE_ID=

# Optional
DISCORD_AUDIT_REASON=External site verification

Likewise, the bot token, guild ID, and role ID should be obtained from the Discord Developer Portal and configured appropriately for your environment.

Warning

The backend server and the Invite Bot/Server are intentionally separated due to bot sharding concerns. The current implementation was not designed with a general distributed environment in mind, so the bot server should be deployed as a separate single instance. This architecture may be improved in the future.

For more details, please refer to the updated source code and documentation.

[yulmwu]

This PR is a mirror of the PR specified in the description. Since SMCTF and N4U Wargame share nearly identical codebases, we will merge it immediately without performing additional code reviews on the already verified code.

[codecov]

Codecov Report

❌ Patch coverage is 70.29703% with 150 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/service/discord_service.go	60.13%	40 Missing and 17 partials ⚠️
internal/discord/client.go	72.72%	19 Missing and 5 partials ⚠️
internal/discord/oauth.go	70.49%	9 Missing and 9 partials ⚠️
internal/http/handlers/errors.go	14.28%	18 Missing ⚠️
internal/http/handlers/discord.go	86.36%	8 Missing and 4 partials ⚠️
internal/config/config.go	84.37%	5 Missing and 5 partials ⚠️
internal/http/router.go	0.00%	7 Missing ⚠️
internal/repo/discord_repo.go	83.33%	2 Missing and 2 partials ⚠️

📢 Thoughts on this report? Let us know!