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import crypto from "node:crypto";
import { z } from "zod";
const zTokenPayload = z.object({
payload: z.unknown(),
expiresAt: z.number(),
});
const zSignedTokenPayload = z.object({
payload: zTokenPayload,
signature: z.string(),
});
/**
* Returns the expiry date aligned to the specified interval.
* If the time left until the next interval is less than the grace period,
* it skips to the following interval.
*
* @param now - The current date and time (defaults to new Date()).
* @param intervalSeconds - The interval in seconds (e.g., 1800 for 30 mins).
* @param gracePeriodSeconds - The grace period in seconds.
* @returns The calculated expiry Date.
*/
export function getAlignedExpiry(
intervalSeconds: number,
gracePeriodSeconds: number,
now: Date = new Date(),
): number {
const ms = now.getTime();
const intervalMs = intervalSeconds * 1000;
// Find the next interval
const nextIntervalTime =
Math.floor(ms / intervalMs) * intervalMs + intervalMs;
// Time left until the next interval
const timeLeft = nextIntervalTime - ms;
// Decide which interval to use
const finalIntervalTime =
timeLeft < gracePeriodSeconds * 1000
? nextIntervalTime + intervalMs
: nextIntervalTime;
return finalIntervalTime;
}
export type SignedTokenPayload = z.infer<typeof zSignedTokenPayload>;
export function createSignedToken(
payload: unknown,
secret: string,
expiryEpoch?: number,
): string {
const expiresAt = expiryEpoch ?? Date.now() + 5 * 60 * 1000; // 5 minutes from now
const toBeSigned: z.infer<typeof zTokenPayload> = {
payload,
expiresAt,
};
const payloadString = JSON.stringify(toBeSigned);
const signature = crypto
.createHmac("sha256", secret)
.update(payloadString)
.digest("hex");
const tokenData: z.infer<typeof zSignedTokenPayload> = {
payload: toBeSigned,
signature,
};
return Buffer.from(JSON.stringify(tokenData)).toString("base64");
}
export function verifySignedToken<T>(
token: string,
secret: string,
schema: z.ZodSchema<T>,
): T | null {
try {
const tokenData = zSignedTokenPayload.parse(
JSON.parse(Buffer.from(token, "base64").toString()),
);
const { payload, signature } = tokenData;
// Verify signature
const expectedSignature = crypto
.createHmac("sha256", secret)
.update(JSON.stringify(payload))
.digest("hex");
if (signature !== expectedSignature) {
return null;
}
// Check expiry
if (Date.now() > payload.expiresAt) {
return null;
}
return schema.parse(payload.payload);
} catch {
return null;
}
}
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