ca groundwork

server/internal/clients/README.md

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+# Client Handshake process
+
+Drop clients need to complete a handshake in order to connect to a Drop server. It also trades certificates for encrypted P2P connections.
+
+## 1. Client requests a handshake
+Client makes request: `POST /api/v1/client/initiate` with information about the client. 
+
+Server responds with a URL to send the user to. It generates a device ID, which has all the metadata attached. 
+
+## 2. User signs in
+Client sends user to the provided URL (in external browser). User signs in using the existing authentication stack. 
+
+Server sends redirect to drop://handshake/[id]/[token], where the token is an authentication token to generate the necessary certificates, and the ID is the client ID as generated by the server. 
+
+## 3. Client requests certificates
+Client makes request: `POST /api/v1/client/handshake` with the token recieved in the previous step. 
+
+The server uses it's CA to generate a public-private key pair, the CN of the client ID. It then sends that pair, plus the CA's public key, to the client, which stores it all. 
+
+The certificate lasts for a year, and is rotated when it has 3 months or less left on it's expiry. 
+
+## 4.a Client requests one-time device endpoint
+The client generates a nonce and signs it with their private key. This is then attached to any device-related request.
+
+## 4.b Client wants a long-lived session
+The client does the same as above, but instead makes the request to `POST /api/v1/client/session`, which generates a session token that lasts for a day. This can then be used in the request to provide authentication. 

server/internal/clients/ca.ts

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+import path from "path";
+import droplet from "@drop/droplet";
+import { CertificateStore } from "./store";
+
+export type CertificateBundle = {
+  priv: string;
+  pub: string;
+  cert: string;
+};
+
+/*
+This is designed to handle client certificates, as described in the README.md
+*/
+export class CertificateAuthority {
+  private certificateStore: CertificateStore;
+
+  private root: CertificateBundle;
+
+  constructor(store: CertificateStore, root: CertificateBundle) {
+    this.certificateStore = store;
+    this.root = root;
+  }
+
+  static async new(store: CertificateStore) {
+    const root = await store.fetch("ca");
+    if (root === undefined) {
+      const [priv, pub, cert] = droplet.generateRootCa();
+      const bundle: CertificateBundle = { priv, pub, cert };
+      await store.store("ca", bundle);
+      return new CertificateAuthority(store, bundle);
+    }
+    return new CertificateAuthority(store, root);
+  }
+}

server/internal/clients/store.ts

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+import path from "path";
+import fs from "fs";
+import { CertificateBundle } from "./ca";
+
+export type CertificateStore = {
+  store(name: string, data: CertificateBundle): Promise<void>;
+  fetch(name: string): Promise<CertificateBundle | undefined>;
+};
+
+export const fsCertificateStore = (base: string) => {
+  const store: CertificateStore = {
+    async store(name: string, data: CertificateBundle) {
+      const filepath = path.join(base, name);
+      fs.writeFileSync(filepath, JSON.stringify(data));
+    },
+    async fetch(name: string) {
+      const filepath = path.join(base, name);
+      if (!fs.existsSync(filepath)) return undefined;
+      return JSON.parse(fs.readFileSync(filepath, "utf-8"));
+    },
+  };
+  return store;
+};