Bug 1863372: Adds begin oauth flow implementation. r=markh,skhamis

Differential Revision: https://phabricator.services.mozilla.com/D192881

services/fxaccounts/FxAccounts.sys.mjs

@@ -45,6 +45,7 @@ ChromeUtils.defineESModuleGetters(lazy, {
   FxAccountsConfig: "resource://gre/modules/FxAccountsConfig.sys.mjs",
   FxAccountsDevice: "resource://gre/modules/FxAccountsDevice.sys.mjs",
   FxAccountsKeys: "resource://gre/modules/FxAccountsKeys.sys.mjs",
+  FxAccountsOAuth: "resource://gre/modules/FxAccountsOAuth.sys.mjs",
   FxAccountsProfile: "resource://gre/modules/FxAccountsProfile.sys.mjs",
   FxAccountsTelemetry: "resource://gre/modules/FxAccountsTelemetry.sys.mjs",
 });
@@ -829,6 +830,14 @@ FxAccountsInternal.prototype = {
     return this._device;
   },
 
+  _oauth: null,
+  get oauth() {
+    if (!this._oauth) {
+      this._oauth = new lazy.FxAccountsOAuth();
+    }
+    return this._oauth;
+  },
+
   _telemetry: null,
   get telemetry() {
     if (!this._telemetry) {

services/fxaccounts/FxAccountsOAuth.sys.mjs

@@ -0,0 +1,143 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import {
+  FX_OAUTH_CLIENT_ID,
+  SCOPE_PROFILE,
+  SCOPE_PROFILE_WRITE,
+  SCOPE_OLD_SYNC,
+} from "resource://gre/modules/FxAccountsCommon.sys.mjs";
+
+const VALID_SCOPES = [SCOPE_PROFILE, SCOPE_PROFILE_WRITE, SCOPE_OLD_SYNC];
+
+/**
+ * Handles all logic and state related to initializing, and completing OAuth flows
+ * with FxA
+ * It's possible to start multiple OAuth flow, but only one can be completed, and once one flow is completed
+ * all the other in-flight flows will be concluded, and attempting to complete those flows will result in errors.
+ */
+export class FxAccountsOAuth {
+  #flow;
+  constructor() {
+    this.#flow = {};
+  }
+
+  /**
+   * Stores a flow in-memory
+   * @param { string } state: A base-64 URL-safe string represnting a random value created at the start of the flow
+   * @param { Object } value: The data needed to complete a flow, once the oauth code is available.
+   * in practice, `value` is:
+   *  - `verifier`: A base=64 URL-safe string representing the PKCE code verifier
+   *  - `key`: The private key need to decrypt the JWE we recieve from the auth server
+   *  - `requestedScopes`: The scopes the caller requested, meant to be compared against the scopes the server authorized
+   */
+  addFlow(state, value) {
+    this.#flow[state] = value;
+  }
+
+  /**
+   * Clears all started flows
+   */
+  clearAllFlows() {
+    this.#flow = {};
+  }
+
+  /*
+   * Gets a stored flow
+   * @param { string } state: The base-64 URL-safe state string that was created at the start of the flow
+   * @returns { Object }: The values initially stored when startign th eoauth flow
+   * in practice, the return value is:
+   *  - `verifier`: A base=64 URL-safe string representing the PKCE code verifier
+   *  - `key`: The private key need to decrypt the JWE we recieve from the auth server
+   *  - ``requestedScopes`: The scopes the caller requested, meant to be compared against the scopes the server authorized
+   */
+  getFlow(state) {
+    return this.#flow[state];
+  }
+
+  /**
+   * Begins an OAuth flow, to be completed with a an OAuth code and state.
+   *
+   * This function stores needed information to complete the flow. You must call `completeOAuthFlow`
+   * on the same instance of `FxAccountsOAuth`, otherwise the completing of the oauth flow will fail.
+   *
+   * @param { string[] } scopes: The OAuth scopes the client should request from FxA
+   *
+   * @returns { Object }: Returns an object representing the query parameters that should be
+   *     added to the FxA authorization URL to initialize an oAuth flow.
+   *     In practice, the query parameters are:
+   *       - `client_id`: The OAuth client ID for Firefox Desktop
+   *       - `scope`: The scopes given by the caller, space seperated
+   *       - `action`: This will always be `email`
+   *       - `response_type`: This will always be `code`
+   *       - `access_type`: This will always be `offline`
+   *       - `state`: A URL-safe base-64 string randomly generated
+   *       - `code_challenge`: A URL-safe base-64 string representing the PKCE challenge
+   *       - `code_challenge_method`: This will always be `S256`
+   *          For more informatio about PKCE, read https://datatracker.ietf.org/doc/html/rfc7636
+   *       - `keys_jwk`: A URL-safe base-64 representing a JWK to be used as a public key by the server
+   *          to generate a JWE
+   */
+  async beginOAuthFlow(scopes) {
+    if (
+      !Array.isArray(scopes) &&
+      scopes.some(scope => !VALID_SCOPES.contains(scope))
+    ) {
+      throw new Error("Invalid scopes");
+    }
+    const queryParams = {
+      client_id: FX_OAUTH_CLIENT_ID,
+      action: "email",
+      response_type: "code",
+      access_type: "offline",
+      scope: scopes.join(" "),
+    };
+
+    // Generate a random, 16 byte value to represent a state that we verify
+    // once we complete the oauth flow, to ensure that we only conclude
+    // an oauth flow that we started
+    const state = new Uint8Array(16);
+    crypto.getRandomValues(state);
+    const stateB64 = ChromeUtils.base64URLEncode(state, { pad: false });
+    queryParams.state = stateB64;
+
+    // Generate a 43 byte code verifier for PKCE, in accordance with
+    // https://datatracker.ietf.org/doc/html/rfc7636#section-7.1 which recommends a
+    // 43-octet URL safe string
+    const codeVerifier = new Uint8Array(43);
+    crypto.getRandomValues(codeVerifier);
+    const codeVerifierB64 = ChromeUtils.base64URLEncode(codeVerifier, {
+      pad: false,
+    });
+    const challenge = await crypto.subtle.digest(
+      "SHA-256",
+      new TextEncoder().encode(codeVerifierB64)
+    );
+    const challengeB64 = ChromeUtils.base64URLEncode(challenge, { pad: false });
+    queryParams.code_challenge = challengeB64;
+    queryParams.code_challenge_method = "S256";
+
+    // Generate a public, private key pair to be used during the oauth flow
+    // to encrypt scoped-keys as they roundtrip through the auth server
+    const ECDH_KEY = { name: "ECDH", namedCurve: "P-256" };
+    const key = await crypto.subtle.generateKey(ECDH_KEY, true, ["deriveKey"]);
+    const publicKey = await crypto.subtle.exportKey("jwk", key.publicKey);
+    const privateKey = key.privateKey;
+
+    // We encode the public key as URL-safe base64 to be included in the query parameters
+    const encodedPublicKey = ChromeUtils.base64URLEncode(
+      new TextEncoder().encode(JSON.stringify(publicKey)),
+      { pad: false }
+    );
+    queryParams.keys_jwk = encodedPublicKey;
+
+    // We store the state in-memory, to verify once the oauth flow is completed
+    this.addFlow(stateB64, {
+      key: privateKey,
+      verifier: codeVerifierB64,
+      requestedScopes: scopes,
+    });
+    return queryParams;
+  }
+}

services/fxaccounts/moz.build

@@ -22,6 +22,7 @@ EXTRA_JS_MODULES += [
     "FxAccountsConfig.sys.mjs",
     "FxAccountsDevice.sys.mjs",
     "FxAccountsKeys.sys.mjs",
+    "FxAccountsOAuth.sys.mjs",
     "FxAccountsPairing.sys.mjs",
     "FxAccountsPairingChannel.sys.mjs",
     "FxAccountsProfile.sys.mjs",

services/fxaccounts/tests/xpcshell/test_oauth_flow.js

@@ -0,0 +1,88 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/* global crypto */
+
+"use strict";
+
+const { FxAccountsOAuth } = ChromeUtils.importESModule(
+  "resource://gre/modules/FxAccountsOAuth.sys.mjs"
+);
+
+const { SCOPE_PROFILE, FX_OAUTH_CLIENT_ID } = ChromeUtils.importESModule(
+  "resource://gre/modules/FxAccountsCommon.sys.mjs"
+);
+
+ChromeUtils.defineESModuleGetters(this, {
+  jwcrypto: "resource://services-crypto/jwcrypto.sys.mjs",
+});
+
+initTestLogging("Trace");
+
+add_task(function test_begin_oauth_flow() {
+  const oauth = new FxAccountsOAuth();
+  add_task(async function test_begin_oauth_flow_invalid_scopes() {
+    try {
+      await oauth.beginOAuthFlow("foo,fi,fum", "foo");
+      Assert.fail("Should have thrown error, scopes must be an array");
+    } catch {
+      // OK
+    }
+    try {
+      await oauth.beginOAuthFlow(["not-a-real-scope", SCOPE_PROFILE]);
+      Assert.fail("Should have thrown an error, must use a valid scope");
+    } catch {
+      // OK
+    }
+  });
+  add_task(async function test_begin_oauth_flow_ok() {
+    const scopes = [SCOPE_PROFILE, SCOPE_OLD_SYNC];
+    const queryParams = await oauth.beginOAuthFlow(scopes);
+
+    // First verify default query parameters
+    Assert.equal(queryParams.client_id, FX_OAUTH_CLIENT_ID);
+    Assert.equal(queryParams.action, "email");
+    Assert.equal(queryParams.response_type, "code");
+    Assert.equal(queryParams.access_type, "offline");
+    Assert.equal(queryParams.scope, [SCOPE_PROFILE, SCOPE_OLD_SYNC].join(" "));
+
+    // Then, we verify that the state is a valid Base64 value
+    const state = queryParams.state;
+    ChromeUtils.base64URLDecode(state, { padding: "reject" });
+
+    // Then, we verify that the codeVerifier, can be used to verify the code_challenge
+    const code_challenge = queryParams.code_challenge;
+    Assert.equal(queryParams.code_challenge_method, "S256");
+    const oauthFlow = oauth.getFlow(state);
+    const codeVerifierB64 = oauthFlow.verifier;
+    const expectedChallenge = await crypto.subtle.digest(
+      "SHA-256",
+      new TextEncoder().encode(codeVerifierB64)
+    );
+    const expectedChallengeB64 = ChromeUtils.base64URLEncode(
+      expectedChallenge,
+      { pad: false }
+    );
+    Assert.equal(expectedChallengeB64, code_challenge);
+
+    // Then, we verify that something encrypted with the `keys_jwk`, can be decrypted using the private key
+    const keysJwk = queryParams.keys_jwk;
+    const decodedKeysJwk = JSON.parse(
+      new TextDecoder().decode(
+        ChromeUtils.base64URLDecode(keysJwk, { padding: "reject" })
+      )
+    );
+    const plaintext = "text to be encrypted and decrypted!";
+    delete decodedKeysJwk.key_ops;
+    const jwe = await jwcrypto.generateJWE(
+      decodedKeysJwk,
+      new TextEncoder().encode(plaintext)
+    );
+    const privateKey = oauthFlow.key;
+    const decrypted = await jwcrypto.decryptJWE(jwe, privateKey);
+    Assert.equal(new TextDecoder().decode(decrypted), plaintext);
+
+    // Finally, we verify that we stored the requested scopes
+    Assert.deepEqual(oauthFlow.requestedScopes, scopes);
+  });
+});

services/fxaccounts/tests/xpcshell/xpcshell.toml

@@ -28,6 +28,8 @@ support-files = [
 
 ["test_loginmgr_storage.js"]
 
+["test_oauth_flow.js"]
+
 ["test_oauth_token_storage.js"]
 
 ["test_oauth_tokens.js"]