feat(auth): make password length configurable via env (min 5–30, max 30–128)

Add PASSWORD_MIN_LENGTH / PASSWORD_MAX_LENGTH (validated in src/env.ts) and a
shared passwordPolicy helper. The policy drives the zod schemas in register,
password reset and the admin create-user dialog, plus the live requirement
checks and strength meter in the register form.

Locale messages now interpolate the configured minimum via {min} instead of
hard-coding 12.

src/lib/auth/password-policy.ts

@@ -0,0 +1,27 @@
+import { env } from "@/env";
+
+/** Hard floor/ceiling so a bad env value can never lock accounts out. */
+const ABSOLUTE_MIN_LENGTH = 5;
+const ABSOLUTE_MAX_LENGTH = 128;
+
+function toLength(value: unknown, fallback: number): number {
+	const parsed = typeof value === "number" ? value : Number(value);
+	return Number.isFinite(parsed) ? Math.trunc(parsed) : fallback;
+}
+
+/**
+ * Effective password-length policy. `PASSWORD_MIN_LENGTH` / `PASSWORD_MAX_LENGTH`
+ * drive the bounds; the values are clamped to a sane window so a typo in the env
+ * can neither accept empty passwords nor reject every possible one.
+ */
+export const passwordPolicy = (() => {
+	const minLength = Math.min(
+		ABSOLUTE_MAX_LENGTH,
+		Math.max(ABSOLUTE_MIN_LENGTH, toLength(env.PASSWORD_MIN_LENGTH, 12)),
+	);
+	const maxLength = Math.max(
+		minLength,
+		Math.min(ABSOLUTE_MAX_LENGTH, toLength(env.PASSWORD_MAX_LENGTH, 128)),
+	);
+	return { minLength, maxLength };
+})();

src/lib/validators/user.test.ts

@@ -12,7 +12,7 @@ describe("createUserSchema", () => {
 		const result = createUserSchema.safeParse({
 			username: "TestUser",
 			mail: "[email protected]",
-			password: "secret123",
+			password: "secret123456",
 		});
 		expect(result.success).toBe(true);
 		if (result.success) {
@@ -26,7 +26,7 @@ describe("createUserSchema", () => {
 			createUserSchema.safeParse({
 				username: "ab",
 				mail: "[email protected]",
-				password: "secret123",
+				password: "secret123456",
 			}).success,
 		).toBe(false);
 	});
@@ -36,7 +36,7 @@ describe("createUserSchema", () => {
 			createUserSchema.safeParse({
 				username: "a".repeat(21),
 				mail: "[email protected]",
-				password: "secret123",
+				password: "secret123456",
 			}).success,
 		).toBe(false);
 	});
@@ -46,7 +46,7 @@ describe("createUserSchema", () => {
 			createUserSchema.safeParse({
 				username: "user@name",
 				mail: "[email protected]",
-				password: "secret123",
+				password: "secret123456",
 			}).success,
 		).toBe(false);
 	});
@@ -56,7 +56,7 @@ describe("createUserSchema", () => {
 			createUserSchema.safeParse({
 				username: "TestUser",
 				mail: "not-an-email",
-				password: "secret123",
+				password: "secret123456",
 			}).success,
 		).toBe(false);
 	});

src/lib/validators/user.ts

@@ -1,4 +1,5 @@
 import { z } from "zod";
+import { passwordPolicy } from "@/lib/auth/password-policy";
 
 export const createUserSchema = z.object({
 	username: z
@@ -10,7 +11,16 @@ export const createUserSchema = z.object({
 			"Username can only contain letters, numbers, _ and -",
 		),
 	mail: z.string().email("Invalid email address"),
-	password: z.string().min(6, "Password must be at least 6 characters"),
+	password: z
+		.string()
+		.min(
+			passwordPolicy.minLength,
+			`Password must be at least ${passwordPolicy.minLength} characters`,
+		)
+		.max(
+			passwordPolicy.maxLength,
+			`Password must be at most ${passwordPolicy.maxLength} characters`,
+		),
 	rank: z.coerce.number().int().min(1).max(7).default(1),
 	motto: z.string().max(127).default(""),
 });