Adds theme to the portal hook

.changeset/hungry-bars-pick.md

@@ -0,0 +1,5 @@
+---
+"@polar-sh/better-auth": minor
+---
+
+Adds theme to the portal hook

packages/polar-betterauth/src/__tests__/plugins/portal.test.ts

@@ -141,6 +141,122 @@ describe("portal plugin", () => {
 				expect.stringContaining("Polar customer portal creation failed"),
 			);
 		});
+
+		it("should apply theme to portal URL when provided", async () => {
+			const plugin = portal({ theme: "dark" });
+			const endpoints = plugin(mockClient);
+			const themeHandler = endpoints.portal.handler;
+
+			const mockSession = {
+				token: "session-token-123",
+				customerPortalUrl: "https://polar.sh/portal/session-123",
+			};
+
+			vi.mocked(mockClient.customerSessions.create).mockResolvedValue(
+				mockSession,
+			);
+
+			const ctx = {
+				context: {
+					session: { user: { id: "user-123" } },
+				},
+				json: vi.fn(),
+			};
+
+			await themeHandler(ctx);
+
+			expect(ctx.json).toHaveBeenCalledWith({
+				url: "https://polar.sh/portal/session-123?theme=dark",
+				redirect: true,
+			});
+		});
+
+		it("should support light theme", async () => {
+			const plugin = portal({ theme: "light" });
+			const endpoints = plugin(mockClient);
+			const themeHandler = endpoints.portal.handler;
+
+			const mockSession = {
+				token: "session-token-123",
+				customerPortalUrl: "https://polar.sh/portal/session-123",
+			};
+
+			vi.mocked(mockClient.customerSessions.create).mockResolvedValue(
+				mockSession,
+			);
+
+			const ctx = {
+				context: {
+					session: { user: { id: "user-123" } },
+				},
+				json: vi.fn(),
+			};
+
+			await themeHandler(ctx);
+
+			expect(ctx.json).toHaveBeenCalledWith({
+				url: "https://polar.sh/portal/session-123?theme=light",
+				redirect: true,
+			});
+		});
+
+		it("should not add theme parameter when not provided", async () => {
+			const plugin = portal();
+			const endpoints = plugin(mockClient);
+			const noThemeHandler = endpoints.portal.handler;
+
+			const mockSession = {
+				token: "session-token-123",
+				customerPortalUrl: "https://polar.sh/portal/session-123",
+			};
+
+			vi.mocked(mockClient.customerSessions.create).mockResolvedValue(
+				mockSession,
+			);
+
+			const ctx = {
+				context: {
+					session: { user: { id: "user-123" } },
+				},
+				json: vi.fn(),
+			};
+
+			await noThemeHandler(ctx);
+
+			expect(ctx.json).toHaveBeenCalledWith({
+				url: "https://polar.sh/portal/session-123",
+				redirect: true,
+			});
+		});
+
+		it("should preserve existing query parameters when adding theme", async () => {
+			const plugin = portal({ theme: "dark" });
+			const endpoints = plugin(mockClient);
+			const themeHandler = endpoints.portal.handler;
+
+			const mockSession = {
+				token: "session-token-123",
+				customerPortalUrl: "https://polar.sh/portal/session-123?foo=bar",
+			};
+
+			vi.mocked(mockClient.customerSessions.create).mockResolvedValue(
+				mockSession,
+			);
+
+			const ctx = {
+				context: {
+					session: { user: { id: "user-123" } },
+				},
+				json: vi.fn(),
+			};
+
+			await themeHandler(ctx);
+
+			expect(ctx.json).toHaveBeenCalledWith({
+				url: "https://polar.sh/portal/session-123?foo=bar&theme=dark",
+				redirect: true,
+			});
+		});
 	});
 
 	describe("state endpoint", () => {

packages/polar-betterauth/src/plugins/portal.ts

@@ -6,10 +6,14 @@ import { z } from "zod";
 
 export interface PortalConfig {
 	returnUrl?: string;
+	/**
+	 * Portal theme
+	 */
+	theme?: "light" | "dark";
 }
 
 export const portal =
-	({ returnUrl }: PortalConfig = {}) =>
+	({ returnUrl, theme }: PortalConfig = {}) =>
 	(polar: Polar) => {
 		const retUrl = returnUrl ? new URL(returnUrl) : undefined;
 
@@ -33,8 +37,14 @@ export const portal =
 							returnUrl: retUrl ? decodeURI(retUrl.toString()) : undefined,
 						});
 
+						const portalUrl = new URL(customerSession.customerPortalUrl);
+
+						if (theme) {
+							portalUrl.searchParams.set("theme", theme);
+						}
+
 						return ctx.json({
-							url: customerSession.customerPortalUrl,
+							url: portalUrl.toString(),
 							redirect: true,
 						});
 					} catch (e: unknown) {