Align backend plan with codebase

lib/server/hash.ts

@@ -0,0 +1,17 @@
+import { createHash, randomBytes } from "crypto";
+
+export function sha256Hex(input: string): string {
+  return createHash("sha256").update(input, "utf8").digest("hex");
+}
+
+export function hashOtpCode(code: string, pepper: string): string {
+  return sha256Hex(`${pepper}:otp:${code}`);
+}
+
+export function hashSessionToken(token: string, pepper: string): string {
+  return sha256Hex(`${pepper}:session:${token}`);
+}
+
+export function newSessionToken(): string {
+  return randomBytes(32).toString("base64url");
+}