CIBA implementation

src/auth/backchannel.ts

@@ -0,0 +1,254 @@
+// Wednesday, 8 January, 2025
+// Client Initiated Backchannel Authentication (CIBA)
+
+// CIBA is an OpenID Foundation standard for a decoupled authentication flow. It enables
+// solution developers to build authentication flows where the user logging in does not do so
+// directly on the device that receives the ID or access tokens (the “Consumption Device”), but
+// instead on a separate “Authorization Device”.
+
+import { JSONApiResponse } from '../lib/models.js';
+import { BaseAuthAPI } from './base-auth-api.js';
+
+/**
+ * The response from the authorize endpoint.
+ */
+export type AuthorizeResponse = {
+  /**
+   * The authorization request ID.
+   */
+  auth_req_id: string;
+  /**
+   * The duration in seconds until the authentication request expires.
+   */
+  expires_in: number;
+  /**
+   * The interval in seconds to wait between poll requests.
+   */
+  interval: number;
+};
+
+type AuthorizeCredentialsPartial = {
+  client_id: string;
+  client_secret?: string;
+  client_assertion?: string;
+  client_assertion_type?: string;
+};
+
+/**
+ * The login hint containing information about the user for authentication.
+ */
+type LoginHint = {
+  /**
+   * The format of the login hint.
+   */
+  format: 'iss_sub';
+  /**
+   * The issuer URL.
+   */
+  iss: string;
+  /**
+   * The subject identifier.
+   */
+  sub: string;
+};
+
+/**
+ * Generates the login hint for the user.
+ *
+ * @param {string} userId - The user ID.
+ * @param {string} domain - The tenant domain.
+ * @returns {string} - The login hint as a JSON string.
+ */
+const getLoginHint = (userId: string, domain: string): string => {
+  // remove trailing '/' from domain, added later for uniformity
+  const trimmedDomain = domain.endsWith('/') ? domain.slice(0, -1) : domain;
+  const loginHint: LoginHint = {
+    format: 'iss_sub',
+    iss: `https://${trimmedDomain}/`,
+    sub: `${userId}`,
+  };
+  return JSON.stringify(loginHint);
+};
+
+/**
+ * Options for the authorize request.
+ */
+export type AuthorizeOptions = {
+  /**
+   * A human-readable string intended to be displayed on both the device calling /bc-authorize and the user’s authentication device.
+   */
+  binding_message: string;
+  /**
+   * A space-separated list of OIDC and custom API scopes.
+   */
+  scope: string;
+  /**
+   * Unique identifier of the audience for an issued token.
+   */
+  audience?: string;
+  /**
+   * Custom expiry time in seconds for this request.
+   */
+  request_expiry?: string;
+  /**
+   * The user ID.
+   */
+  userId: string;
+  /**
+   * Optional parameter for subject issuer context.
+   */
+  subjectIssuerContext?: string;
+};
+
+type AuthorizeRequest = Omit<AuthorizeOptions, 'userId'> &
+  AuthorizeCredentialsPartial & {
+    login_hint: string;
+  };
+
+/**
+ * The response from the token endpoint.
+ */
+export type TokenResponse = {
+  /**
+   * The access token.
+   */
+  access_token: string;
+  /**
+   * The refresh token, available with the `offline_access` scope.
+   */
+  refresh_token?: string;
+  /**
+   * The user's ID Token.
+   */
+  id_token: string;
+  /**
+   * The token type of the access token.
+   */
+  token_type?: string;
+  /**
+   * The duration in seconds that the access token is valid.
+   */
+  expires_in: number;
+  /**
+   * The scopes associated with the token.
+   */
+  scope: string;
+};
+
+/**
+ * Options for the token request.
+ */
+export type TokenOptions = {
+  /**
+   * The authorization request ID.
+   */
+  auth_req_id: string;
+};
+
+type TokenRequestBody = AuthorizeCredentialsPartial & {
+  auth_req_id: string;
+  grant_type: string;
+};
+
+/**
+ * Interface for the backchannel authentication.
+ */
+export interface IBackchannel {
+  authorize: (options: AuthorizeOptions) => Promise<AuthorizeResponse>;
+  backchannelGrant: (options: TokenOptions) => Promise<TokenResponse>;
+}
+
+const CIBA_GRANT_TYPE = 'urn:openid:params:grant-type:ciba';
+const CIBA_AUTHORIZE_URL = '/bc-authorize';
+const CIBA_TOKEN_URL = '/oauth/token';
+
+/**
+ * Class implementing the backchannel authentication flow.
+ */
+export class Backchannel extends BaseAuthAPI implements IBackchannel {
+  /**
+   * Initiates a CIBA authorization request.
+   *
+   * @param {AuthorizeOptions} options - The options for the request.
+   * @returns {Promise<AuthorizeResponse>} - The authorization response.
+   *
+   * @throws {Error} - If the request fails.
+   */
+  async authorize({ userId, ...options }: AuthorizeOptions): Promise<AuthorizeResponse> {
+    const body: AuthorizeRequest = {
+      ...options,
+      login_hint: getLoginHint(userId, this.domain),
+      client_id: this.clientId,
+    };
+
+    await this.addClientAuthentication(body);
+
+    const response = await this.request.bind(this)(
+      {
+        path: CIBA_AUTHORIZE_URL,
+        method: 'POST',
+        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+        body: new URLSearchParams(body),
+      },
+      {}
+    );
+
+    const r: JSONApiResponse<AuthorizeResponse> = await JSONApiResponse.fromResponse(response);
+    return r.data;
+  }
+
+  /**
+   * Handles the backchannel grant flow for authentication. Client can poll this method at regular intervals to check if the backchannel auth request has been approved.
+   *
+   * @param {string} auth_req_id - The authorization request ID. This value is returned from the call to /bc-authorize. Once you have exchanged an auth_req_id for an ID and access token, it is no longer usable.
+   * @returns {Promise<TokenResponse>} - A promise that resolves to the token response.
+   *
+   * @throws {Error} - Throws an error if the request fails.
+   *
+   * If the authorizing user has not yet approved or rejected the request, you will receive a response like this:
+   * ```json
+   * {
+   *   "error": "authorization_pending",
+   *   "error_description": "The end-user authorization is pending"
+   * }
+   * ```
+   *
+   * If the authorizing user rejects the request, you will receive a response like this:
+   * ```json
+   * {
+   *   "error": "access_denied",
+   *   "error_description": "The end-user denied the authorization request or it has been expired"
+   * }
+   * ```
+   *
+   * If you are polling too quickly (faster than the interval value returned from /bc-authorize), you will receive a response like this:
+   * ```json
+   * {
+   *   "error": "slow_down",
+   *   "error_description": "You are polling faster than allowed. Try again in 10 seconds."
+   * }
+   * ```
+   */
+  async backchannelGrant({ auth_req_id }: TokenOptions): Promise<TokenResponse> {
+    const body: TokenRequestBody = {
+      client_id: this.clientId,
+      auth_req_id,
+      grant_type: CIBA_GRANT_TYPE,
+    };
+
+    await this.addClientAuthentication(body);
+
+    const response = await this.request.bind(this)(
+      {
+        path: CIBA_TOKEN_URL,
+        method: 'POST',
+        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+        body: new URLSearchParams(body),
+      },
+      {}
+    );
+
+    const r: JSONApiResponse<TokenResponse> = await JSONApiResponse.fromResponse(response);
+    return r.data;
+  }
+}

src/auth/index.ts

@@ -1,3 +1,4 @@
+import { Backchannel } from './backchannel.js';
 import { AuthenticationClientOptions } from './base-auth-api.js';
 import { Database } from './database.js';
 import { OAuth } from './oauth.js';
@@ -13,10 +14,12 @@ export class AuthenticationClient {
   database: Database;
   oauth: OAuth;
   passwordless: Passwordless;
+  backchannel: Backchannel;
 
   constructor(options: AuthenticationClientOptions) {
     this.database = new Database(options);
     this.oauth = new OAuth(options);
     this.passwordless = new Passwordless(options);
+    this.backchannel = new Backchannel(options);
   }
 }