Slack Auth & Security

OAuth 2.0 Flow

Bot Token vs User Token

Bot Token (xoxb-):

• Performs actions as the bot user
• Requires bot scopes
• Recommended for most operations

User Token (xoxp-):

• Acts on behalf of specific user
• Requires user scopes
• Used for user-specific operations

Basic OAuth Flow

import "github.com/slack-go/slack"

// Step 1: Generate authorization URL
state := generateRandomState()
authURL := fmt.Sprintf(
    "https://slack.com/oauth/v2/authorize?client_id=%s&scope=%s&state=%s",
    clientID,
    "chat:write,channels:read",
    state,
)

See oauth-flow.md for complete OAuth implementation.

Token Management

Storing Tokens Securely

// NEVER hardcode tokens
// Use environment variables or secrets manager
token := os.Getenv("SLACK_BOT_TOKEN")
api := slack.New(token)

Token Rotation

// Rotate tokens periodically
newToken, err := api.RotateTokens(refreshToken)
if err != nil {
    return err
}

// Update stored token
storeToken(newToken)

See token-management.md for storage strategies and rotation patterns.

Scopes and Permissions

Required Scopes by Operation

Messaging:

• chat:write - Send messages
• chat:write.public - Post to channels bot isn't in

Channels:

• channels:read - View public channels
• channels:manage - Create/manage channels
• groups:read - View private channels

Users:

• users:read - View users
• users:read.email - View user emails

See scopes-permissions.md for comprehensive scope guide.

Security Best Practices

1. Request Verification

Always verify requests from Slack:

import "github.com/slack-go/slack"

func verifySlackRequest(r *http.Request, signingSecret string) bool {
    verifier, err := slack.NewSecretsVerifier(r.Header, signingSecret)
    if err != nil {
        return false
    }

    body, _ := ioutil.ReadAll(r.Body)
    verifier.Write(body)

    return verifier.Ensure() == nil
}

2. HTTPS Only

Never use HTTP endpoints for webhooks:

• ✅ https://your-app.com/slack/events
• ❌ http://your-app.com/slack/events

3. Token Storage

• Use environment variables for development
• Use secrets managers (AWS Secrets Manager, HashiCorp Vault) for production
• Encrypt tokens at rest
• Never commit tokens to version control

4. Rate Limiting

Implement rate limiting to avoid abuse:

type RateLimiter struct {
    requests map[string][]time.Time
    mu       sync.Mutex
}

func (rl *RateLimiter) Allow(userID string, maxRequests int, window time.Duration) bool {
    rl.mu.Lock()
    defer rl.mu.Unlock()

    now := time.Now()
    cutoff := now.Add(-window)

    // Remove old requests
    var validRequests []time.Time
    for _, t := range rl.requests[userID] {
        if t.After(cutoff) {
            validRequests = append(validRequests, t)
        }
    }

    if len(validRequests) >= maxRequests {
        return false
    }

    rl.requests[userID] = append(validRequests, now)
    return true
}

Multi-Workspace Installations

Token Per Workspace

Store tokens separately for each workspace:

type WorkspaceToken struct {
    TeamID      string
    BotToken    string
    BotUserID   string
    InstalledAt time.Time
}

func getAPIForTeam(teamID string) (*slack.Client, error) {
    token, err := loadTokenForTeam(teamID)
    if err != nil {
        return nil, err
    }
    return slack.New(token.BotToken), nil
}

App Manifest API

Programmatically configure apps:

manifest := &slack.Manifest{
    DisplayInformation: slack.ManifestDisplayInformation{
        Name: "My Bot",
        Description: "Helpful bot",
    },
    Features: slack.ManifestFeatures{
        BotUser: &slack.ManifestBotUser{
            DisplayName: "mybot",
            AlwaysOnline: true,
        },
    },
    OAuthConfig: slack.ManifestOAuthConfig{
        Scopes: slack.ManifestOAuthScopes{
            Bot: []string{"chat:write", "channels:read"},
        },
    },
}

_, err := api.CreateManifest(manifest)

See manifest-api.md for manifest patterns.

Production Checklist

See security-checklist.md for comprehensive security audit:

• ✅ HTTPS endpoints
• ✅ Request signature verification
• ✅ Token encryption at rest
• ✅ Rate limiting
• ✅ Audit logging
• ✅ Error handling (don't leak sensitive info)
• ✅ Regular token rotation

Common Pitfalls

• Hardcoding tokens in code
• Not verifying request signatures
• Using HTTP instead of HTTPS
• Storing tokens in plain text
• Not implementing rate limiting
• Exposing sensitive errors to users