PostHog Data Handling

Overview

Privacy-safe analytics with PostHog. Covers property sanitization to strip PII before events leave the browser, consent-based tracking (opt-in/opt-out), GDPR data subject access requests and deletion, and PostHog's built-in privacy controls (IP masking, session recording masking).

Prerequisites

• PostHog project with current privacy, retention, and deletion capabilities verified for its deployment model
• posthog-js and/or posthog-node installed
• Privacy policy covering analytics data collection
• Cookie consent mechanism (e.g., CookieConsent banner)

Authentication

• Browser capture uses the public project token; do not treat it as a secret or grant it private API access.
• Subject-access, export, and deletion operations use a least-privilege personal API key or OAuth token against the private regional API host.
• Load private credentials from a server-side secret manager, redact them from logs, and never expose them through client bundles or analytics properties.
• Confirm the target project ID and US or EU region before any destructive privacy operation.

Instructions

Tool discipline

Use Read to inspect the relevant configuration and implementation before proposing changes. Use Write only for a new, explicitly requested artifact inside the target project. Use Edit for minimal changes to existing project files after the evidence pass.

Step 1: Privacy-Safe Initialization

import posthog from 'posthog-js';

posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
  api_host: 'https://us.i.posthog.com',

  // Disable autocapture to control exactly what's captured
  autocapture: false,

  // Respect browser Do Not Track setting
  respect_dnt: true,

  // Don't capture until user consents
  opt_out_capturing_by_default: false, // Set true for opt-in model

  // Sanitize ALL properties before they leave the browser
  sanitize_properties: (properties, eventName) => {
    // Remove IP address
    delete properties['$ip'];

    // Remove potentially identifying properties
    delete properties['$device_id'];

    // Redact URLs containing tokens or auth info
    if (properties['$current_url']) {
      properties['$current_url'] = properties['$current_url']
        .replace(/token=[^&]+/g, 'token=[REDACTED]')
        .replace(/key=[^&]+/g, 'key=[REDACTED]')
        .replace(/session=[^&]+/g, 'session=[REDACTED]');
    }

    // Redact referrer tokens
    if (properties['$referrer']) {
      properties['$referrer'] = properties['$referrer']
        .replace(/token=[^&]+/g, 'token=[REDACTED]');
    }

    return properties;
  },

  // Session recording privacy
  session_recording: {
    maskAllInputs: true,           // Mask all input fields
    maskTextSelector: '.pii-data', // Mask specific elements
  },
});

Step 2: Consent-Based Tracking

// Cookie consent integration
interface ConsentState {
  analytics: boolean;
  functional: boolean;
  marketing: boolean;
}

export function handleConsentChange(consent: ConsentState) {
  if (consent.analytics) {
    // User opted in — start capturing
    posthog.opt_in_capturing();
  } else {
    // User opted out — stop capturing and clear local data
    posthog.opt_out_capturing();
    posthog.reset(); // Clears distinct_id, device_id, session data
  }
}

// Check consent before identifying (PII)
export function identifyWithConsent(
  userId: string,
  properties: Record<string, any>,
  hasAnalyticsConsent: boolean
) {
  if (!hasAnalyticsConsent) return;

  // Only send non-PII properties by default
  const safeProperties: Record<string, any> = {
    plan: properties.plan,
    signup_date: properties.signupDate,
    account_type: properties.accountType,
    // Do NOT include: email, name, phone, address
  };

  posthog.identify(userId, safeProperties);
}

// On page load: restore consent state
export function restoreConsent() {
  const consent = getCookieConsent(); // Your consent mechanism
  if (consent?.analytics === false) {
    posthog.opt_out_capturing();
  }
}

Step 3: GDPR Data Subject Access Request (SAR)

// Find a person by email and export their data
async function handleSubjectAccessRequest(email: string) {
  const personalKey = process.env.POSTHOG_PERSONAL_API_KEY!;
  const projectId = process.env.POSTHOG_PROJECT_ID!;

  // 1. Find the person by email property
  const searchResponse = await fetch(
    `https://us.posthog.com/api/projects/${projectId}/persons/?properties=[{"key":"email","value":"${encodeURIComponent(email)}","type":"person"}]`,
    { headers: { Authorization: `Bearer ${personalKey}` } }
  );
  const searchData = await searchResponse.json();

  if (!searchData.results?.length) {
    return { found: false, message: 'No person found with that email' };
  }

  const person = searchData.results[0];
  const distinctId = person.distinct_ids[0];

  // 2. Export their events (strip PII from export)
  const eventsResponse = await fetch(
    `https://us.posthog.com/api/projects/${projectId}/query/`,
    {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${personalKey}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        query: {
          kind: 'HogQLQuery',
          query: `SELECT event, timestamp, properties FROM events WHERE distinct_id = '${distinctId}' ORDER BY timestamp DESC LIMIT 1000`,
        },
      }),
    }
  );
  const eventsData = await eventsResponse.json();

  return {
    found: true,
    person: {
      distinct_ids: person.distinct_ids,
      properties: person.properties,
      created_at: person.created_at,
    },
    events_count: eventsData.results?.length || 0,
    events: eventsData.results,
  };
}

Step 4: GDPR Right to Erasure (Data Deletion)

// Delete a person and all their events
async function handleDeletionRequest(email: string) {
  const personalKey = process.env.POSTHOG_PERSONAL_API_KEY!;
  const projectId = process.env.POSTHOG_PROJECT_ID!;

  // 1. Find the person
  const searchResponse = await fetch(
    `https://us.posthog.com/api/projects/${projectId}/persons/?properties=[{"key":"email","value":"${encodeURIComponent(email)}","type":"person"}]`,
    { headers: { Authorization: `Bearer ${personalKey}` } }
  );
  const searchData = await searchResponse.json();

  if (!searchData.results?.length) {
    return { deleted: false, reason: 'Person not found' };
  }

  const personId = searchData.results[0].id;

  // 2. Delete the person (PostHog also deletes associated events)
  const deleteResponse = await fetch(
    `https://us.posthog.com/api/projects/${projectId}/persons/${personId}/`,
    {
      method: 'DELETE',
      headers: { Authorization: `Bearer ${personalKey}` },
    }
  );

  if (!deleteResponse.ok) {
    throw new Error(`Deletion failed: ${deleteResponse.status}`);
  }

  return {
    deleted: true,
    personId,
    timestamp: new Date().toISOString(),
  };
}

Step 5: Property Filtering for Data Exports

// Strip PII from HogQL query results before exporting
const BLOCKED_PROPERTIES = ['$ip', 'email', 'phone', 'name', 'address', 'ssn'];

async function safeExport(hogql: string) {
  const response = await fetch(
    `https://us.posthog.com/api/projects/${process.env.POSTHOG_PROJECT_ID}/query/`,
    {
      method: 'POST',
      headers: {
        Authorization: `Bearer ${process.env.POSTHOG_PERSONAL_API_KEY}`,
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({ query: { kind: 'HogQLQuery', query: hogql } }),
    }
  );
  const data = await response.json();

  // Remove blocked columns from results
  if (data.columns && data.results) {
    const blockedIndexes = new Set(
      data.columns.map((col: string, i: number) =>
        BLOCKED_PROPERTIES.some(b => col.toLowerCase().includes(b)) ? i : -1
      ).filter((i: number) => i >= 0)
    );

    data.columns = data.columns.filter((_: string, i: number) => !blockedIndexes.has(i));
    data.results = data.results.map((row: any[]) =>
      row.filter((_: any, i: number) => !blockedIndexes.has(i))
    );
  }

  return data;
}

Error Handling

GDPR Compliance Checklist

• [ ] sanitize_properties strips PII before events leave browser
• [ ] Consent mechanism with opt_in_capturing / opt_out_capturing
• [ ] respect_dnt: true in PostHog init
• [ ] Session recording masks all inputs
• [ ] Subject Access Request handler implemented
• [ ] Data Deletion handler implemented
• [ ] Privacy policy updated to mention PostHog analytics

Output

• Privacy-safe PostHog initialization with property sanitization
• Consent-based tracking with opt-in/opt-out
• GDPR Subject Access Request handler
• GDPR Data Deletion handler
• PII-safe data export function

Examples

For a consent-gated web app, start opted out, enable capture only after the consent signal, mask sensitive elements, reject prohibited properties before send, and test both consent states. Produce a data map and identify any deletion step that requires private-API authorization.

Resources

See official PostHog references for current authority and verification boundaries.

• PostHog Privacy Controls
• PostHog GDPR Compliance
• PostHog Persons API
• PostHog Data Collection Controls