auth.js

import {
  getTokenExpiresAtDate,
  isBrowserEnv,
  createBrowserSafeString,
  OAuth2AuthorizationUrl,
  OAuth2TokenUrl,
  isWorkerEnv,
} from './utils.js';
import { parseResponse } from './response.js';

let fetch;
let crypto;
let Encoder;

// Expiration is 300 seconds but needs to be in milliseconds for Date object
const TokenExpirationBuffer = 300 * 1000;
const PKCELength = 128;
const TokenAccessTypes = ['legacy', 'offline', 'online'];
const GrantTypes = ['code', 'token'];
const IncludeGrantedScopes = ['none', 'user', 'team'];

/**
 * @class DropboxAuth
 * @classdesc The DropboxAuth class that provides methods to manage, acquire, and refresh tokens.
 * @arg {Object} options
 * @arg {Function} [options.fetch] - fetch library for making requests.
 * @arg {String} [options.accessToken] - An access token for making authenticated
 * requests.
 * @arg {Date} [options.AccessTokenExpiresAt] - Date of the current access token's
 * expiration (if available)
 * @arg {String} [options.refreshToken] - A refresh token for retrieving access tokens
 * @arg {String} [options.clientId] - The client id for your app. Used to create
 * authentication URL.
 * @arg {String} [options.clientSecret] - The client secret for your app. Used to create
 * authentication URL and refresh access tokens.
 * @arg {String} [options.domain] - A custom domain to use when making api requests. This
 * should only be used for testing as scaffolding to avoid making network requests.
 * @arg {String} [options.domainDelimiter] - A custom delimiter to use when separating domain from
 * subdomain. This should only be used for testing as scaffolding.
 * @arg {Object} [options.customHeaders] - An object (in the form of header: value) designed to set
 * custom headers to use during a request.
 * @arg {Boolean} [options.dataOnBody] - Whether request data is sent on body or as URL params.
  * Defaults to false.
*/
export default class DropboxAuth {
  constructor(options) {
    options = options || {};

    if (isBrowserEnv()) {
      fetch = window.fetch.bind(window);
      crypto = window.crypto || window.msCrypto; // for IE11
    } else if (isWorkerEnv()) {
      /* eslint-disable no-restricted-globals */
      fetch = self.fetch.bind(self);
      crypto = self.crypto;
      /* eslint-enable no-restricted-globals */
    } else {
      fetch = require('node-fetch'); // eslint-disable-line global-require
      crypto = require('crypto'); // eslint-disable-line global-require
    }

    if (typeof TextEncoder === 'undefined') {
      Encoder = require('util').TextEncoder; // eslint-disable-line global-require
    } else {
      Encoder = TextEncoder;
    }

    this.fetch = options.fetch || fetch;
    this.accessToken = options.accessToken;
    this.accessTokenExpiresAt = options.accessTokenExpiresAt;
    this.refreshToken = options.refreshToken;
    this.clientId = options.clientId;
    this.clientSecret = options.clientSecret;

    this.domain = options.domain;
    this.domainDelimiter = options.domainDelimiter;
    this.customHeaders = options.customHeaders;
    this.dataOnBody = options.dataOnBody;
  }

  /**
     * Set the access token used to authenticate requests to the API.
     * @arg {String} accessToken - An access token
     * @returns {undefined}
     */
  setAccessToken(accessToken) {
    this.accessToken = accessToken;
  }

  /**
     * Get the access token
     * @returns {String} Access token
     */
  getAccessToken() {
    return this.accessToken;
  }

  /**
     * Set the client id, which is used to help gain an access token.
     * @arg {String} clientId - Your apps client id
     * @returns {undefined}
     */
  setClientId(clientId) {
    this.clientId = clientId;
  }

  /**
     * Get the client id
     * @returns {String} Client id
     */
  getClientId() {
    return this.clientId;
  }

  /**
     * Set the client secret
     * @arg {String} clientSecret - Your app's client secret
     * @returns {undefined}
     */
  setClientSecret(clientSecret) {
    this.clientSecret = clientSecret;
  }

  /**
     * Get the client secret
     * @returns {String} Client secret
     */
  getClientSecret() {
    return this.clientSecret;
  }

  /**
     * Gets the refresh token
     * @returns {String} Refresh token
     */
  getRefreshToken() {
    return this.refreshToken;
  }

  /**
     * Sets the refresh token
     * @param refreshToken - A refresh token
     */
  setRefreshToken(refreshToken) {
    this.refreshToken = refreshToken;
  }

  /**
     * Gets the access token's expiration date
     * @returns {Date} date of token expiration
     */
  getAccessTokenExpiresAt() {
    return this.accessTokenExpiresAt;
  }

  /**
     * Sets the access token's expiration date
     * @param accessTokenExpiresAt - new expiration date
     */
  setAccessTokenExpiresAt(accessTokenExpiresAt) {
    this.accessTokenExpiresAt = accessTokenExpiresAt;
  }

  /**
     * Sets the code verifier for PKCE flow
     * @param {String} codeVerifier - new code verifier
     */
  setCodeVerifier(codeVerifier) {
    this.codeVerifier = codeVerifier;
  }

  /**
     * Gets the code verifier for PKCE flow
     * @returns {String} - code verifier for PKCE
     */
  getCodeVerifier() {
    return this.codeVerifier;
  }

  generateCodeChallenge() {
    const encoder = new Encoder();
    const codeData = encoder.encode(this.codeVerifier);
    let codeChallenge;
    if (isBrowserEnv() || isWorkerEnv()) {
      return crypto.subtle.digest('SHA-256', codeData)
        .then((digestedHash) => {
          const base64String = btoa(String.fromCharCode.apply(null, new Uint8Array(digestedHash)));
          codeChallenge = createBrowserSafeString(base64String).substr(0, 128);
          this.codeChallenge = codeChallenge;
        });
    }
    const digestedHash = crypto.createHash('sha256').update(codeData).digest();
    codeChallenge = createBrowserSafeString(digestedHash);
    this.codeChallenge = codeChallenge;
    return Promise.resolve();
  }

  generatePKCECodes() {
    let codeVerifier;
    if (isBrowserEnv() || isWorkerEnv()) {
      const array = new Uint8Array(PKCELength);
      const randomValueArray = crypto.getRandomValues(array);
      const base64String = btoa(randomValueArray);
      codeVerifier = createBrowserSafeString(base64String).substr(0, 128);
    } else {
      const randomBytes = crypto.randomBytes(PKCELength);
      codeVerifier = createBrowserSafeString(randomBytes).substr(0, 128);
    }
    this.codeVerifier = codeVerifier;

    return this.generateCodeChallenge();
  }

  /**
     * Get a URL that can be used to authenticate users for the Dropbox API.
     * @arg {String} redirectUri - A URL to redirect the user to after
     * authenticating. This must be added to your app through the admin interface.
     * @arg {String} [state] - State that will be returned in the redirect URL to help
     * prevent cross site scripting attacks.
     * @arg {String} [authType] - auth type, defaults to 'token', other option is 'code'
     * @arg {String} [tokenAccessType] - type of token to request.  From the following:
     * null - creates a token with the app default (either legacy or online)
     * legacy - creates one long-lived token with no expiration
     * online - create one short-lived token with an expiration
     * offline - create one short-lived token with an expiration with a refresh token
     * @arg {Array<String>} [scope] - scopes to request for the grant
     * @arg {String} [includeGrantedScopes] - whether or not to include previously granted scopes.
     * From the following:
     * user - include user scopes in the grant
     * team - include team scopes in the grant
     * Note: if this user has never linked the app, include_granted_scopes must be None
     * @arg {boolean} [usePKCE] - Whether or not to use Sha256 based PKCE. PKCE should be only use
     * on client apps which doesn't call your server. It is less secure than non-PKCE flow but
     * can be used if you are unable to safely retrieve your app secret
     * @returns {Promise<String>} - Url to send user to for Dropbox API authentication
     * returned in a promise
     */
  getAuthenticationUrl(redirectUri, state, authType = 'token', tokenAccessType = null, scope = null, includeGrantedScopes = 'none', usePKCE = false) {
    const clientId = this.getClientId();
    const baseUrl = OAuth2AuthorizationUrl(this.domain);

    if (!clientId) {
      throw new Error('A client id is required. You can set the client id using .setClientId().');
    }
    if (authType !== 'code' && !redirectUri) {
      throw new Error('A redirect uri is required.');
    }
    if (!GrantTypes.includes(authType)) {
      throw new Error('Authorization type must be code or token');
    }
    if (tokenAccessType && !TokenAccessTypes.includes(tokenAccessType)) {
      throw new Error('Token Access Type must be legacy, offline, or online');
    }
    if (scope && !(scope instanceof Array)) {
      throw new Error('Scope must be an array of strings');
    }
    if (!IncludeGrantedScopes.includes(includeGrantedScopes)) {
      throw new Error('includeGrantedScopes must be none, user, or team');
    }

    let authUrl;
    if (authType === 'code') {
      authUrl = `${baseUrl}?response_type=code&client_id=${clientId}`;
    } else {
      authUrl = `${baseUrl}?response_type=token&client_id=${clientId}`;
    }

    if (redirectUri) {
      authUrl += `&redirect_uri=${redirectUri}`;
    }
    if (state) {
      authUrl += `&state=${state}`;
    }
    if (tokenAccessType) {
      authUrl += `&token_access_type=${tokenAccessType}`;
    }
    if (scope) {
      authUrl += `&scope=${scope.join(' ')}`;
    }
    if (includeGrantedScopes !== 'none') {
      authUrl += `&include_granted_scopes=${includeGrantedScopes}`;
    }
    if (usePKCE) {
      return this.generatePKCECodes()
        .then(() => {
          authUrl += '&code_challenge_method=S256';
          authUrl += `&code_challenge=${this.codeChallenge}`;
          return authUrl;
        });
    }
    return Promise.resolve(authUrl);
  }

  /**
     * Get an OAuth2 access token from an OAuth2 Code.
     * @arg {String} redirectUri - A URL to redirect the user to after
     * authenticating. This must be added to your app through the admin interface.
     * @arg {String} code - An OAuth2 code.
     * @returns {Object} An object containing the token and related info (if applicable)
     */
  getAccessTokenFromCode(redirectUri, code) {
    const clientId = this.getClientId();
    const clientSecret = this.getClientSecret();

    if (!clientId) {
      throw new Error('A client id is required. You can set the client id using .setClientId().');
    }
    let path = OAuth2TokenUrl(this.domain, this.domainDelimiter);
    path += '?grant_type=authorization_code';
    path += `&code=${code}`;
    path += `&client_id=${clientId}`;

    if (clientSecret) {
      path += `&client_secret=${clientSecret}`;
    } else {
      if (!this.codeVerifier) {
        throw new Error('You must use PKCE when generating the authorization URL to not include a client secret');
      }
      path += `&code_verifier=${this.codeVerifier}`;
    }
    if (redirectUri) {
      path += `&redirect_uri=${redirectUri}`;
    }

    const fetchOptions = {
      method: 'POST',
      headers: {
        'Content-Type': 'application/x-www-form-urlencoded',
      },
    };
    return this.fetch(path, fetchOptions)
      .then((res) => parseResponse(res));
  }

  /**
     * Checks if a token is needed, can be refreshed and if the token is expired.
     * If so, attempts to refresh access token
     * @returns {Promise<*>}
     */
  checkAndRefreshAccessToken() {
    const canRefresh = this.getRefreshToken() && this.getClientId();
    const needsRefresh = !this.getAccessTokenExpiresAt()
            || (new Date(Date.now() + TokenExpirationBuffer)) >= this.getAccessTokenExpiresAt();
    const needsToken = !this.getAccessToken();
    if ((needsRefresh || needsToken) && canRefresh) {
      return this.refreshAccessToken();
    }
    return Promise.resolve();
  }

  /**
     * Refreshes the access token using the refresh token, if available
     * @arg {Array<String>} scope - a subset of scopes from the original
     * refresh to acquire with an access token
     * @returns {Promise<*>}
     */
  refreshAccessToken(scope = null) {
    const clientId = this.getClientId();
    const clientSecret = this.getClientSecret();

    if (!clientId) {
      throw new Error('A client id is required. You can set the client id using .setClientId().');
    }
    if (scope && !(scope instanceof Array)) {
      throw new Error('Scope must be an array of strings');
    }

    let refreshUrl = OAuth2TokenUrl(this.domain, this.domainDelimiter);
    const fetchOptions = {
      headers: { 'Content-Type': 'application/json' },
      method: 'POST',
    };

    if (this.dataOnBody) {
      const body = { grant_type: 'refresh_token', client_id: clientId, refresh_token: this.getRefreshToken() };

      if (clientSecret) {
        body.client_secret = clientSecret;
      }
      if (scope) {
        body.scope = scope.join(' ');
      }

      fetchOptions.body = body;
    } else {
      refreshUrl += `?grant_type=refresh_token&refresh_token=${this.getRefreshToken()}`;
      refreshUrl += `&client_id=${clientId}`;
      if (clientSecret) {
        refreshUrl += `&client_secret=${clientSecret}`;
      }
      if (scope) {
        refreshUrl += `&scope=${scope.join(' ')}`;
      }
    }

    return this.fetch(refreshUrl, fetchOptions)
      .then((res) => parseResponse(res))
      .then((res) => {
        this.setAccessToken(res.result.access_token);
        this.setAccessTokenExpiresAt(getTokenExpiresAtDate(res.result.expires_in));
      });
  }
}