jwt.ts

import * as base64url from 'https://deno.land/std@0.144.0/encoding/base64url.ts';
import * as base64 from 'https://deno.land/std@0.144.0/encoding/base64.ts';

export type Header = {
    alg: 'RS256';
    [key: string]: unknown;
};

export type Payload = {
    iss: string;
    aud: string;
    exp: number;
    iat: number;
    scope: string;
};

const encoder = new TextEncoder();

export default async function (
    header: Header,
    payload: Payload,
    secret: string,
): Promise<string> {
    const encodedHeader = base64url.encode(JSON.stringify(header));
    const encodedPayload = base64url.encode(JSON.stringify(payload));
    const data = encoder.encode(`${encodedHeader}.${encodedPayload}`);

    const cleanedKey = secret.replace(
        /^\n?-----BEGIN PRIVATE KEY-----\n?|\n?-----END PRIVATE KEY-----\n?$/g,
        '',
    );
    const decodedKey = base64.decode(cleanedKey).buffer;
    const key = await crypto.subtle.importKey(
        'pkcs8',
        decodedKey,
        { name: 'RSASSA-PKCS1-v1_5', hash: 'SHA-256' },
        true,
        ['sign'],
    );

    const signature = await crypto.subtle.sign(
        { hash: { name: 'SHA-256' }, name: 'RSASSA-PKCS1-v1_5' },
        key,
        data,
    );
    const encodedSignature = base64url.encode(signature);
    return `${encodedHeader}.${encodedPayload}.${encodedSignature}`;
}