platformservice/ts/mta/mta.classes.emailsignjob.ts

import * as plugins from '../plugins.js';
import type { MtaService } from './mta.classes.mta.js';

interface Headers {
  [key: string]: string;
}

interface IEmailSignJobOptions {
  domain: string;
  selector: string;
  headers: Headers;
  body: string;
}

export class EmailSignJob {
  mtaRef: MtaService;
  jobOptions: IEmailSignJobOptions;

  constructor(mtaRefArg: MtaService, options: IEmailSignJobOptions) {
    this.mtaRef = mtaRefArg;
    this.jobOptions = options;
  }

  async loadPrivateKey(): Promise<string> {
    return plugins.fs.promises.readFile(
      (await this.mtaRef.dkimCreator.getKeyPathsForDomain(this.jobOptions.domain)).privateKeyPath,
      'utf-8'
    );
  }

  public async getSignatureHeader(emailMessage: string): Promise<string> {
    const signResult = await plugins.dkimSign(emailMessage, {
      // Optional, default canonicalization, default is "relaxed/relaxed"
      canonicalization: 'relaxed/relaxed', // c=

      // Optional, default signing and hashing algorithm
      // Mostly useful when you want to use rsa-sha1, otherwise no need to set
      algorithm: 'rsa-sha256',

      // Optional, default is current time
      signTime: new Date(), // t=

      // Keys for one or more signatures
      // Different signatures can use different algorithms (mostly useful when
      // you want to sign a message both with RSA and Ed25519)
      signatureData: [
        {
          signingDomain: this.jobOptions.domain, // d=
          selector: this.jobOptions.selector, // s=
          // supported key types: RSA, Ed25519
          privateKey: await this.loadPrivateKey(), // k=

          // Optional algorithm, default is derived from the key.
          // Overrides whatever was set in parent object
          algorithm: 'rsa-sha256',

          // Optional signature specifc canonicalization, overrides whatever was set in parent object
          canonicalization: 'relaxed/relaxed', // c=

          // Maximum number of canonicalized body bytes to sign (eg. the "l=" tag).
          // Do not use though. This is available only for compatibility testing.
          // maxBodyLength: 12345
        },
      ],
    });
    const signature = signResult.signatures;
    return signature;
  }
}