Skip user creation when customer has conflict externalID

packages/polar-betterauth/src/hooks/customer.ts

@@ -74,3 +74,19 @@ export const onUserUpdate =
 			}
 		}
 	};
+
+export const beforeUserCreate =
+	(options: PolarOptions) =>
+	async (user: User, ctx?: GenericEndpointContext) => {
+		if (ctx && options.skipUserOnExternalIDConflict) {
+			const { result: existingCustomers } = await options.client.customers.list(
+				{ email: user.email },
+			);
+			const existingCustomer = existingCustomers.items[0];
+			if (existingCustomer && existingCustomer.externalId !== user.id) {
+				throw new APIError("CONFLICT", {
+					message: `Customer with email ${user.email} already exists with a different external ID.`,
+				});
+			}
+		}
+	};

packages/polar-betterauth/src/index.ts

@@ -1,5 +1,5 @@
 import type { BetterAuthPlugin } from "better-auth";
-import { onUserCreate, onUserUpdate } from "./hooks/customer";
+import { beforeUserCreate, onUserCreate, onUserUpdate } from "./hooks/customer";
 import type { PolarEndpoints, PolarOptions } from "./types";
 
 export { polarClient } from "./client";
@@ -28,6 +28,7 @@ export const polar = <O extends PolarOptions>(options: O) => {
 					databaseHooks: {
 						user: {
 							create: {
+								before: beforeUserCreate(options),
 								after: onUserCreate(options),
 							},
 							update: {

packages/polar-betterauth/src/types.ts

@@ -32,10 +32,12 @@ export interface PolarOptions {
 	 * Polar Client
 	 */
 	client: Polar;
+
 	/**
 	 * Enable customer creation when a user signs up
 	 */
 	createCustomerOnSignUp?: boolean;
+
 	/**
 	 * A custom function to get the customer create
 	 * params
@@ -50,6 +52,12 @@ export interface PolarOptions {
 	) => Promise<{
 		metadata?: Record<string, string>;
 	}>;
+
+	/**
+	 * Do not create a new user if polar customer exists with different externalId
+	 */
+	skipUserOnExternalIDConflict?: boolean;
+
 	/**
 	 * Use Polar plugins
 	 */