fix: retry login across deploy cutovers

src/components/auth/home-login-form.tsx

@@ -8,6 +8,7 @@ import {
 	CaptchaWidget,
 	readCaptchaToken,
 } from "@/components/auth/captcha-widget";
+import { signInWithTransientRetry } from "@/lib/auth/sign-in-retry";
 
 export function HomeLoginForm({
 	captcha = { provider: "none" },
@@ -49,12 +50,14 @@ export function HomeLoginForm({
 					return;
 				}
 			}
-			const res = await signIn("credentials", {
-				username,
-				password,
-				code,
-				redirect: false,
-			});
+			const res = await signInWithTransientRetry(() =>
+				signIn("credentials", {
+					username,
+					password,
+					code,
+					redirect: false,
+				}),
+			);
 			if (!res || res.error) {
 				setError(
 					needs2fa ? "Invalid 2FA code" : "Invalid username or password",
@@ -62,6 +65,8 @@ export function HomeLoginForm({
 				return;
 			}
 			window.location.href = "/";
+		} catch {
+			setError(needs2fa ? "Invalid 2FA code" : "Invalid username or password");
 		} finally {
 			setPending(false);
 		}

src/components/auth/login-form.tsx

@@ -10,6 +10,7 @@ import {
 	CaptchaWidget,
 	readCaptchaToken,
 } from "@/components/auth/captcha-widget";
+import { signInWithTransientRetry } from "@/lib/auth/sign-in-retry";
 
 export function LoginForm({
 	captcha = { provider: "none" },
@@ -52,12 +53,14 @@ export function LoginForm({
 					return;
 				}
 			}
-			const res = await signIn("credentials", {
-				username,
-				password,
-				code,
-				redirect: false,
-			});
+			const res = await signInWithTransientRetry(() =>
+				signIn("credentials", {
+					username,
+					password,
+					code,
+					redirect: false,
+				}),
+			);
 			if (!res || res.error) {
 				setError(
 					needs2fa ? t("errorInvalid2fa") : t("errorInvalidCredentials"),
@@ -65,6 +68,8 @@ export function LoginForm({
 				return;
 			}
 			window.location.href = "/me";
+		} catch {
+			setError(needs2fa ? t("errorInvalid2fa") : t("errorInvalidCredentials"));
 		} finally {
 			setPending(false);
 		}

src/lib/auth/sign-in-retry.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it, vi } from "vitest";
+import { signInWithTransientRetry } from "./sign-in-retry";
+
+describe("signInWithTransientRetry", () => {
+	it("retries thrown transport errors with a short backoff", async () => {
+		const transportError = new SyntaxError("unexpected character in JSON");
+		const signIn = vi
+			.fn<() => Promise<{ ok: boolean }>>()
+			.mockRejectedValueOnce(transportError)
+			.mockRejectedValueOnce(transportError)
+			.mockResolvedValue({ ok: true });
+		const wait = vi.fn(async () => undefined);
+
+		await expect(signInWithTransientRetry(signIn, wait)).resolves.toEqual({
+			ok: true,
+		});
+		expect(signIn).toHaveBeenCalledTimes(3);
+		expect(wait).toHaveBeenNthCalledWith(1, 400);
+		expect(wait).toHaveBeenNthCalledWith(2, 800);
+	});
+
+	it("returns ordinary auth responses without retrying", async () => {
+		const response = { ok: false, error: "CredentialsSignin" };
+		const signIn = vi.fn(async () => response);
+		const wait = vi.fn(async () => undefined);
+
+		await expect(signInWithTransientRetry(signIn, wait)).resolves.toBe(
+			response,
+		);
+		expect(signIn).toHaveBeenCalledOnce();
+		expect(wait).not.toHaveBeenCalled();
+	});
+
+	it("rethrows the last transport error after four attempts", async () => {
+		const transportError = new Error("temporary upstream failure");
+		const signIn = vi
+			.fn<() => Promise<never>>()
+			.mockRejectedValue(transportError);
+		const wait = vi.fn(async () => undefined);
+
+		await expect(signInWithTransientRetry(signIn, wait)).rejects.toBe(
+			transportError,
+		);
+		expect(signIn).toHaveBeenCalledTimes(4);
+		expect(wait).toHaveBeenCalledTimes(3);
+	});
+});

src/lib/auth/sign-in-retry.ts

@@ -0,0 +1,25 @@
+type Wait = (delayMs: number) => Promise<unknown>;
+
+const waitForDelay: Wait = (delayMs) =>
+	new Promise((resolve) => setTimeout(resolve, delayMs));
+
+export async function signInWithTransientRetry<T>(
+	signIn: () => Promise<T>,
+	wait: Wait = waitForDelay,
+): Promise<T> {
+	const maxAttempts = 4;
+
+	for (let attempt = 0; attempt < maxAttempts; attempt++) {
+		try {
+			return await signIn();
+		} catch (error) {
+			if (attempt === maxAttempts - 1) {
+				throw error;
+			}
+
+			await wait(400 * 2 ** attempt);
+		}
+	}
+
+	throw new Error("Unreachable auth retry state");
+}