docs: add activeOrganizationId on org schema

demo/nextjs/lib/auth.ts

@@ -18,6 +18,7 @@ import { MysqlDialect } from "kysely";
 import { createPool } from "mysql2/promise";
 import { nextCookies } from "better-auth/next-js";
 import { customSession } from "./auth/plugins/custom-session";
+import { addAccountToSession } from "./plugin";
 
 const from = process.env.BETTER_AUTH_EMAIL || "delivered@resend.dev";
 const to = process.env.TEST_EMAIL || "";
@@ -155,6 +156,6 @@ export const auth = betterAuth({
 		oneTap(),
 		oAuthProxy(),
 		nextCookies(),
-		customSession(),
+		addAccountToSession,
 	],
 });

demo/nextjs/lib/plugin.ts

@@ -0,0 +1,40 @@
+import { BetterAuthPlugin } from "better-auth";
+
+export const addAccountToSession = {
+	id: "add-account-to-session",
+	hooks: {
+		after: [
+			{
+				matcher(context) {
+					return context.path.startsWith("/callback");
+				},
+				async handler(ctx) {
+					const sessionCookie = ctx.responseHeader.get(
+						ctx.context.authCookies.sessionToken.name,
+					);
+					if (!sessionCookie) {
+						return;
+					}
+					const provider = ctx.path.split("/callback")[1];
+					if (!provider) {
+						return;
+					}
+					const sessionId = sessionCookie.split(".")[0];
+					await ctx.context.internalAdapter.updateSession(sessionId, {
+						accountId: provider,
+					});
+				},
+			},
+		],
+	},
+	schema: {
+		session: {
+			fields: {
+				accountId: {
+					type: "string",
+					required: false,
+				},
+			},
+		},
+	},
+} satisfies BetterAuthPlugin;