feat: function to create self-delegated app-side signers

This means, they already include the self-delegation authorization from the encryptor

packages/taco-auth/src/providers/encryptor/self-delegate.ts

@@ -1,20 +1,53 @@
-import { ethers } from 'ethers';
+import { ethers, Wallet } from 'ethers';
 import { z } from 'zod';
 
+// import { Bytes } from "@ethersproject/bytes";
+
 import { AuthSignature } from '../../auth-sig';
 import { LocalStorage } from '../../storage';
 
 export const ENCRYPTOR_SELF_DELEGATE_AUTH_METHOD = 'EncryptorSelfDelegate'
 
 export const SelfDelegateTypedDataSchema = z.string();
 
+
+// TODO: Create generic EncryptorSigner class/interface, which can be 
+// instantiated with ethers' Signers and Wallets, but also with our custom
+// classes
+export class DelegatedSigner extends Wallet {  // TODO: extend from generic Signer
+
+  authSignature?: AuthSignature;
+
+  async authenticate(selfDelegateProvider: SelfDelegateProvider){
+    const appSideSignerAddress = await this.getAddress();
+    this.authSignature = await selfDelegateProvider.getOrCreateAuthSignature(appSideSignerAddress);
+  }
+
+  override async signMessage(message: any): Promise<string> {  // TODO: Restrict input type to Bytes | string
+    if (typeof this.authSignature === 'undefined'){
+      throw new Error('Encryptor must authenticate app signer first');
+    }
+    const appSignature = await super.signMessage(message);
+    return appSignature.concat(this.authSignature.signature)
+  }
+}
+
+
 export class SelfDelegateProvider {
   private readonly storage: LocalStorage;
 
   constructor(private readonly signer: ethers.Signer) {
     this.storage = new LocalStorage();
   }
 
+  public async createSelfDelegatedAppSideSigner(
+    ephemeralPrivateKey: any  // TODO: Find a stricter type
+  ): Promise<DelegatedSigner> {
+    const appSideSigner = new DelegatedSigner(ephemeralPrivateKey);
+    await appSideSigner.authenticate(this);
+    return appSideSigner;
+  }
+
   public async getOrCreateAuthSignature(
     ephemeralPublicKeyOrAddress: string
   ): Promise<AuthSignature> {

packages/taco-auth/test/auth-provider.test.ts

@@ -140,11 +140,18 @@ describe('encryptor self-delegate provider authorization', () => {
   const provider = fakeProvider(bobSecretKeyBytes);
   const signer = provider.getSigner();
   const selfDelegateProvider = new SelfDelegateProvider(signer);
+
+  it('creates a new self-delegated app signer', async () => {
+    const appSideSignerAddress = await applicationSideSigner.getAddress();
+    const [newSigner, newAuthSignature] = await selfDelegateProvider.createSelfDelegatedAppSideSigner(aliceSecretKeyBytes);
+    expect(await newSigner.getAddress()).toEqual(appSideSignerAddress);
+    expect(newAuthSignature.typedData).toEqual(appSideSignerAddress);
+  });
 
   const applicationSideProvider = fakeProvider(aliceSecretKeyBytes);
   const applicationSideSigner = applicationSideProvider.getSigner();
 
-  it('creates a new  message', async () => {
+  it('creates a new auth signature', async () => {
     const appSideSignerAddress = await applicationSideSigner.getAddress();
     const typedSignature = await selfDelegateProvider.getOrCreateAuthSignature(appSideSignerAddress);
     expect(typedSignature.signature).toBeDefined();