npm install better-auth @polar-sh/better-auth @polar-sh/sdk
# or
yarn add better-auth @polar-sh/better-auth @polar-sh/sdk
# or
pnpm add better-auth @polar-sh/better-auth @polar-sh/sdk

POLAR_ACCESS_TOKEN=polar_oat_...
POLAR_WEBHOOK_SECRET=...

import { betterAuth } from "better-auth";
import {
  polar,
  checkout,
  portal,
  usage,
  webhooks,
} from "@polar-sh/better-auth";
import { Polar } from "@polar-sh/sdk";

const polarClient = new Polar({
  accessToken: process.env.POLAR_ACCESS_TOKEN,
  server: "sandbox", // Use 'sandbox' for testing, defaults to 'production'
});

const auth = betterAuth({
  plugins: [
    polar({
      client: polarClient,
      createCustomerOnSignUp: true, // Auto-create Polar customer
      // Optional: Custom metadata for new customers
      getCustomerCreateParams: ({ user }, request) => ({
        metadata: { source: "better-auth" },
      }),
      use: [
        // 1. Checkout Plugin
        checkout({
          products: [{ productId: "prod_123", slug: "pro" }],
          successUrl: "/success?checkout_id={CHECKOUT_ID}",
          authenticatedUsersOnly: true,
          returnUrl: "https://myapp.com",
          theme: "dark", // 'light' or 'dark'
        }),

        // 2. Customer Portal Plugin
        portal({
          returnUrl: "https://myapp.com",
        }),

        // 3. Usage Billing Plugin
        usage(),

        // 4. Webhooks Plugin
        webhooks({
          secret: process.env.POLAR_WEBHOOK_SECRET,
          onOrderPaid: (payload) => console.log("💸 Order Paid:", payload),
          onCustomerStateChanged: (payload) =>
            console.log("👤 State Changed:", payload),
          onPayload: (payload) => console.log("📨 Other Event:", payload),
        }),
      ],
    }),
  ],
});

import { createAuthClient } from "better-auth/react";
import { polarClient } from "@polar-sh/better-auth";

export const authClient = createAuthClient({
  plugins: [polarClient()],
});

await authClient.checkout({
  // Option A: Use slug defined in config
  slug: "pro",
  // Option B: Use direct Product ID
  products: ["prod_123"],
  // Optional: Link to an Organization (B2B)
  referenceId: "org_123",
});

await authClient.usage.ingestion({
  event: "ai_generation", // Must match Meter definition in Dashboard
  metadata: {
    tokens: 156,
    model: "gpt-4",
  },
});

const { data: meters } = await authClient.usage.meters.list({
  query: { page: 1, limit: 10 },
});
// Returns: consumed units, credited units, current balance

// Redirects user to Polar Customer Portal
await authClient.customer.portal();

const { data: state } = await authClient.customer.state();

// List Active Subscriptions
const { data: subs } = await authClient.customer.subscriptions.list({
  query: { active: true },
});

// List Orders (Purchases)
const { data: orders } = await authClient.customer.orders.list();

// List Benefits
const { data: benefits } = await authClient.customer.benefits.list();

import { polar, webhooks } from "@polar-sh/better-auth";

const auth = betterAuth({
  plugins: [
    polar({
      client: polarClient,
      use: [
        webhooks({
          secret: process.env.POLAR_WEBHOOK_SECRET,
          // Handlers
          onCustomerStateChanged: (payload) => {
            console.log("Customer state changed:", payload);
          },
          onOrderPaid: (payload) => {
            console.log("Order paid:", payload);
          },
          // ... over 25+ handlers available
          onPayload: (payload) => {
            console.log("Catch-all event:", payload);
          },
        }),
      ],
    }),
  ],
});

const auth = betterAuth({
  user: {
    deleteUser: {
      enabled: true,
      afterDelete: async (user) => {
        await polarClient.customers.deleteExternal({
          externalId: user.id,
        });
      },
    },
  },
});

const orgId = (await authClient.organization.list())?.data?.[0]?.id;

const { data: orders } = await authClient.customer.orders.list({
  query: {
    active: true,
    referenceId: orgId, // Filter by Org ID
  },
});

const hasAccess = orders.length > 0;