feat(Slack Node): Allow users to configure OAuth2 scopes

[Joffcom]

Summary

Replaces the previously hardcoded OAuth2 user_scope list in the Slack credential with a user-configurable field. By default, the credential behaves identically to before — the same full set of user scopes is requested automatically. Users who need a restricted or custom scope set can enable the Custom Scopes toggle to expose and edit the User Scope field before connecting.

Changes:

• Adds customScopes boolean toggle (default: false) to the Slack OAuth2 credential
• Adds userScope string field (shown when customScopes is true) pre-populated with the default scope list
• Adds an explicit empty scope hidden field to prevent bot-scope inheritance from the base credential
• Updates authQueryParameters to dynamically use the custom userScope when enabled, or fall back to the default scope list otherwise
• Adds unit tests for the credential properties

To test:

1. Create a new Slack OAuth2 credential — verify it works unchanged with default scopes
2. Enable Custom Scopes, remove a scope, re-authorize — verify only the specified scopes are requested

Related Linear tickets, Github issues, and Community forum posts

https://linear.app/n8n/issue/NODE-3815

Review / Merge checklist

• I have seen this code, I have run this code, and I take responsibility for this code.
• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with Backport to Beta, Backport to Stable, or Backport to v1 (if the PR is an urgent fix that needs to be backported)

🤖 PR Summary generated by AI

Tested locally on 2.16 without this then ran with this with various reconnect options to ensure this doesn't break anything by removing the bot scope under the scopes field. We removed this as it can't be used in the node to send messages as the bot user.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[cubic-dev-ai]

No issues found across 2 files

Architecture diagram

sequenceDiagram
    participant User as User (Browser)
    participant UI as n8n Credential UI
    participant Server as n8n Server (OAuth Engine)
    participant Slack as Slack Auth Server

    Note over User,UI: Configuration Phase
    User->>UI: Toggle "Custom Scopes" (NEW)
    UI-->>User: Show "User Scope" field (NEW)
    User->>UI: Modify scopes in "User Scope" field
    
    Note over User,Slack: Authorization Flow
    User->>UI: Click "Connect my account"
    UI->>Server: Initialize OAuth2 Flow
    
    Server->>Server: Evaluate authQueryParameters expression (CHANGED)
    
    alt customScopes is TRUE
        Server->>Server: Use values from "User Scope" field
    else customScopes is FALSE (Default)
        Server->>Server: Use internal default userScope list
    end

    Note right of Server: CHANGED: 'scope' parameter set to empty string<br/>to prevent bot-scope inheritance.

    Server-->>User: Redirect to Slack Authorization URL
    User->>Slack: GET /authorize?user_scope={selected_scopes}&scope=
    
    Note over Slack,User: Slack Consent Screen
    Slack-->>User: Show requested user-level permissions
    User->>Slack: Approve permissions
    
    Slack-->>Server: Callback with Code
    Server->>Slack: POST /api/oauth.v2.access (Exchange code for token)
    Slack-->>Server: Return Access Token
    Server-->>UI: Credential Saved Successfully

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[github-actions]

Performance Comparison

Comparing current → latest master → 14-day baseline

Idle baseline with Instance AI module loaded

Metric	Current	Latest Master	Baseline (avg)	vs Master	vs Baseline	Status
instance-ai-rss-baseline	302.15 MB	354.18 MB	364.79 MB (σ 21.08)	-14.7%	-17.2%	🔴
instance-ai-heap-used-baseline	187.36 MB	191.65 MB	187.79 MB (σ 2.07)	-2.2%	-0.2%	✅

docker-stats

Metric	Current	Latest Master	Baseline (avg)	vs Master	vs Baseline	Status
docker-image-size-n8n	1280.00 MB	1300.48 MB	1303.55 MB (σ 51.48)	-1.6%	-1.8%	✅
docker-image-size-runners	388.00 MB	388.00 MB	391.15 MB (σ 9.26)	+0.0%	-0.8%	✅

Memory consumption baseline with starter plan resources

Metric	Current	Latest Master	Baseline (avg)	vs Master	vs Baseline	Status
memory-heap-used-baseline	115.02 MB	118.98 MB	115.72 MB (σ 2.02)	-3.3%	-0.6%	✅
memory-rss-baseline	223.79 MB	293.85 MB	291.38 MB (σ 29.40)	-23.8%	-23.2%	🔴

How to read this table

• Current: This PR's value (or latest master if PR perf tests haven't run)
• Latest Master: Most recent nightly master measurement
• Baseline: Rolling 14-day average from master
• vs Master: PR impact (current vs latest master)
• vs Baseline: Drift from baseline (current vs rolling avg)
• Status: ✅ within 1σ | ⚠️ 1-2σ | 🔴 >2σ regression

[DawidMyslak]

Looks good overall, 2 minor comments 🙏

[n8n-assistant]

Got released with n8n@2.20.0