Signer

A Signer is an interface that normalizes token signing logic. Its role is to take some content, produce a signature, then later verify that this signature matches the expected content.

It does not embed any business validation. It does not manage claims, expiration, audience, or the full token lifecycle. It only encapsulates the sign and verify mechanics.

The idea is to move this logic away from plain utility functions and encapsulate it in a clear, reusable contract. The tokenHandler then builds on that contract to create a complete flow around the token.

A signer can be used in two ways:

• as an already configured signer, ready to sign and verify;
• as a signer creator, so configuration can be provided later.

Example

import { Signer } from "@duplojs/json-web-token";

const createCustomSigner = Signer.factory(
	"CUSTOM",
	(params: { secret: string }, algorithm) => ({
		sign(content) {
			return `${algorithm}:${params.secret}:${content}`;
		},
		verify(content, signature) {
			return signature === `${algorithm}:${params.secret}:${content}`;
		},
	}),
);

const signer = createCustomSigner({
	secret: "my-secret",
});

const signature = await signer.sign("user:1");
const isValid = await signer.verify("user:1", signature);

Syntax

Signer

interface Signer<
	GenericAlgorithm extends string = string
> {
	readonly algorithm: GenericAlgorithm;
	sign(content: string): MaybePromise<string>;
	verify(content: string, signature: string): MaybePromise<boolean>;
}

CreateSigner

CreateSigner is a function that receives parameters and returns a Signer.

interface CreateSigner<
	GenericAlgorithm extends string,
	GenericParams extends unknown,
> {
	readonly algorithm: GenericAlgorithm;
	(params: NoInfer<GenericParams>): Signer<GenericAlgorithm>;
}

Signer.factory

The factory creates a CreateSigner from your own methods.

function factory<
	const GenericAlgorithm extends string,
	GenericMethodsParams extends unknown,
>(
	algorithm: GenericAlgorithm,
	methods: (
		params: GenericMethodsParams,
		algorithm: NoInfer<GenericAlgorithm>,
	) => {
		sign(content: string): MaybePromise<string>;
		verify(content: string, signature: string): MaybePromise<boolean>;
	},
): CreateSigner<GenericAlgorithm, GenericMethodsParams>;

Built-in signers

The library already provides several ready-to-use signer creators.

HMAC

• Signer.createHS256
• Signer.createHS512

Both signers use a shared secret.

RSA

• Signer.createRS256
• Signer.createRS512

Both signers use a privateKey to sign and a publicKey to verify.