Langfuse Security Basics

Langfuse Security Basics

Overview

Security best practices for Langfuse API keys, data privacy, and compliance.

Prerequisites

• Langfuse SDK installed
• Understanding of API key management
• Knowledge of data privacy requirements (GDPR, etc.)

Instructions

Step 1: Secure API Key Management

# NEVER commit API keys to git
echo '.env*' >> .gitignore
echo '!.env.example' >> .gitignore

# Create .env.example with placeholders
cat > .env.example << 'EOF'
# Langfuse Configuration
LANGFUSE_PUBLIC_KEY=pk-lf-your-public-key
LANGFUSE_SECRET_KEY=sk-lf-your-secret-key
LANGFUSE_HOST=https://cloud.langfuse.com
EOF

# Verify no secrets in git history
git log --all --full-history -- '*/​.env*' '*.env'

Step 2: Use Environment-Specific Keys

// config/​langfuse.ts
interface LangfuseConfig {
  publicKey: string;
  secretKey: string;
  host: string;
  enabled: boolean;
}

function getLangfuseConfig(): LangfuseConfig {
  const env = process.env.NODE_ENV || "development";

  // Different keys per environment
  const configs: Record<string, LangfuseConfig> = {
    development: {
      publicKey: process.env.LANGFUSE_PUBLIC_KEY_DEV!,
      secretKey: process.env.LANGFUSE_SECRET_KEY_DEV!,
      host: process.env.LANGFUSE_HOST_DEV || "https://cloud.langfuse.com",
      enabled: true,
    },
    staging: {
      publicKey: process.env.LANGFUSE_PUBLIC_KEY_STAGING!,
      secretKey: process.env.LANGFUSE_SECRET_KEY_STAGING!,
      host: process.env.LANGFUSE_HOST_STAGING || "https://cloud.langfuse.com",
      enabled: true,
    },
    production: {
      publicKey: process.env.LANGFUSE_PUBLIC_KEY_PROD!,
      secretKey: process.env.LANGFUSE_SECRET_KEY_PROD!,
      host: process.env.LANGFUSE_HOST || "https://cloud.langfuse.com",
      enabled: true,
    },
  };

  return configs[env] || configs.development;
}

Step 3: Implement PII Scrubbing

interface ScrubConfig {
  patterns: RegExp[];
  replacement: string;
}

const DEFAULT_SCRUB_CONFIG: ScrubConfig = {
  patterns: [
    // Email addresses
    /\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b/​g,
    // Phone numbers
    /\b\d{3}[-.]?\d{3}[-.]?\d{4}\b/​g,
    // SSN
    /\b\d{3}-\d{2}-\d{4}\b/​g,
    // Credit card numbers
    /\b\d{4}[-\s]?\d{4}[-\s]?\d{4}[-\s]?\d{4}\b/​g,
    // API keys
    /\b(sk|pk|api|key|token|secret)[-_]?[a-zA-Z0-9]{20,}\b/​gi,
    // IP addresses
    /\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b/​g,
  ],
  replacement: "[REDACTED]",
};

function scrubPII(data: any, config = DEFAULT_SCRUB_CONFIG): any {
  if (typeof data === "string") {
    let scrubbed = data;
    for (const pattern of config.patterns) {
      scrubbed = scrubbed.replace(pattern, config.replacement);
    }
    return scrubbed;
  }

  if (Array.isArray(data)) {
    return data.map((item) => scrubPII(item, config));
  }

  if (typeof data === "object" && data !== null) {
    const scrubbed: Record<string, any> = {};
    for (const [key, value] of Object.entries(data)) {
      // Scrub sensitive field names
      if (/​password|secret|token|key|auth/​i.test(key)) {
        scrubbed[key] = "[REDACTED]";
      } else {
        scrubbed[key] = scrubPII(value, config);
      }
    }
    return scrubbed;
  }

  return data;
}

// Usage
const trace = langfuse.trace({
  name: "user-query",
  input: scrubPII(userInput),
  metadata: scrubPII(metadata),
});

Step 4: Create Secure Trace Wrapper

interface SecureTraceOptions {
  scrubInputs?: boolean;
  scrubOutputs?: boolean;
  excludeFields?: string[];
  allowedMetadataFields?: string[];
}

function createSecureLangfuse(
  config: ConstructorParameters<typeof Langfuse>[0],
  securityOptions: SecureTraceOptions = {}
) {
  const langfuse = new Langfuse(config);

  const {
    scrubInputs = true,
    scrubOutputs = true,
    excludeFields = ["password", "token", "apiKey", "secret"],
    allowedMetadataFields = ["userId", "sessionId", "environment"],
  } = securityOptions;

  function sanitize(data: any, shouldScrub: boolean): any {
    if (!shouldScrub) return data;

    // Remove excluded fields
    if (typeof data === "object" && data !== null) {
      const sanitized = { ...data };
      for (const field of excludeFields) {
        delete sanitized[field];
      }
      return scrubPII(sanitized);
    }

    return scrubPII(data);
  }

  function filterMetadata(
    metadata: Record<string, any>
  ): Record<string, any> {
    const filtered: Record<string, any> = {};
    for (const field of allowedMetadataFields) {
      if (metadata[field] !== undefined) {
        filtered[field] = metadata[field];
      }
    }
    return filtered;
  }

  return {
    trace(params: Parameters<typeof langfuse.trace>[0]) {
      return langfuse.trace({
        ...params,
        input: sanitize(params.input, scrubInputs),
        output: params.output ? sanitize(params.output, scrubOutputs) : undefined,
        metadata: params.metadata
          ? filterMetadata(params.metadata)
          : undefined,
      });
    },

    flush: () => langfuse.flushAsync(),
    shutdown: () => langfuse.shutdownAsync(),
  };
}

Step 5: Implement Key Rotation

// scripts/​rotate-langfuse-keys.ts
import { Langfuse } from "langfuse";

async function rotateKeys() {
  // 1. Generate new keys in Langfuse dashboard
  console.log("1. Create new API keys in Langfuse dashboard");
  console.log("   https://cloud.langfuse.com/​settings/​api-keys\n");

  // 2. Update secrets in your secret manager
  console.log("2. Update secrets in your environment:");
  console.log("   - AWS Secrets Manager");
  console.log("   - GCP Secret Manager");
  console.log("   - HashiCorp Vault");
  console.log("   - GitHub Secrets\n");

  // 3. Deploy with new keys
  console.log("3. Deploy application with new keys\n");

  // 4. Verify new keys work
  const langfuse = new Langfuse({
    publicKey: process.env.LANGFUSE_PUBLIC_KEY_NEW!,
    secretKey: process.env.LANGFUSE_SECRET_KEY_NEW!,
  });

  const trace = langfuse.trace({
    name: "key-rotation-test",
    metadata: { test: true },
  });

  await langfuse.flushAsync();
  console.log("4. Verified new keys work\n");

  // 5. Revoke old keys
  console.log("5. Revoke old keys in Langfuse dashboard");
  console.log("   https://cloud.langfuse.com/​settings/​api-keys\n");

  console.log("Key rotation complete!");
}

rotateKeys().catch(console.error);

Output

• Secure API key management
• Environment-specific key separation
• PII scrubbing for inputs/​outputs
• Secure trace wrapper
• Key rotation procedure

Security Checklist

Error Handling

Examples

Secrets Manager Integration

import { SecretsManager } from "@aws-sdk/​client-secrets-manager";

const secretsManager = new SecretsManager({ region: "us-east-1" });

async function getLangfuseSecrets() {
  const response = await secretsManager.getSecretValue({
    SecretId: "langfuse/​production",
  });

  const secrets = JSON.parse(response.SecretString!);

  return {
    publicKey: secrets.LANGFUSE_PUBLIC_KEY,
    secretKey: secrets.LANGFUSE_SECRET_KEY,
  };
}

// Initialize Langfuse with secrets from manager
const secrets = await getLangfuseSecrets();
const langfuse = new Langfuse(secrets);

Audit Key Usage

// Track which keys are used where
const trace = langfuse.trace({
  name: "operation",
  metadata: {
    keyPrefix: process.env.LANGFUSE_PUBLIC_KEY?.slice(0, 10),
    environment: process.env.NODE_ENV,
    service: process.env.SERVICE_NAME,
  },
});

Resources

• Langfuse Security
• GDPR Compliance
• Langfuse Self-Hosting

Next Steps

For production readiness, see langfuse-prod-checklist.