element-call/src/livekit/openIDSFU.ts

/*
Copyright 2023, 2024 New Vector Ltd.

SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
Please see LICENSE in the repository root for full details.
*/

import { type IOpenIDToken, type MatrixClient } from "matrix-js-sdk";
import { type CallMembershipIdentityParts } from "matrix-js-sdk/lib/matrixrtc/EncryptionManager";
import { type Logger } from "matrix-js-sdk/lib/logger";

import { FailToGetOpenIdToken } from "../utils/errors";
import { doNetworkOperationWithRetry } from "../utils/matrix";
import { Config } from "../config/Config";

/**
 * Configuration and access tokens provided by the SFU on successful authentication.
 */
export interface SFUConfig {
  url: string;
  jwt: string;
  livekitAlias: string;
  // NOTE: Currently unused.
  livekitIdentity: string;
}

/**
 * Decoded details from the JWT.
 */
interface SFUJWTPayload {
  /**
   * Expiration time for the JWT.
   * Note: This value is in seconds since Unix epoch.
   */
  exp: number;
  /**
   * Name of the instance which authored the JWT
   */
  iss: string;
  /**
   * Time at which the JWT can start to be used.
   * Note: This value is in seconds since Unix epoch.
   */
  nbf: number;
  /**
   * Subject. The Livekit alias in this context.
   */
  sub: string;
  /**
   * The set of permissions for the user.
   */
  video: {
    canPublish: boolean;
    canSubscribe: boolean;
    room: string;
    roomJoin: boolean;
  };
}

// The bits we need from MatrixClient
export type OpenIDClientParts = Pick<
  MatrixClient,
  "getOpenIdToken" | "getDeviceId"
>;
/**
 * Gets a bearer token from the homeserver and then use it to authenticate
 * to the matrix RTC backend in order to get acces to the SFU.
 * It has built-in retry for calls to the homeserver with a backoff policy.
 * @param client The Matrix client
 * @param membership Our own membership identity parts used to send to jwt service.
 * @param serviceUrl The URL of the livekit SFU service
 * @param forceOldJwtEndpoint This will use the old jwt endpoint which will create the rtc backend identity based on string concatination
 * instead of a hash.
 * This function by default uses whatever is possible with the current jwt service installed next to the SFU.
 * For remote connections this does not matter, since we will not publish there we can rely on the newest option.
 * For our own connection we can only use the hashed version if we also send the new matrix2.0 sticky events.
 * @param roomId The room id used in the jwt request. This is NOT the livekit_alias. The jwt service will provide the alias. It maps matrix room ids <-> Livekit aliases.
 * @param delayEndpointBaseUrl The URL of the matrix homeserver.
 * @param delayId The delay id used for the jwt service to manage.
 * @param logger optional logger.
 * @returns Object containing the token information
 * @throws FailToGetOpenIdToken
 */
export async function getSFUConfigWithOpenID(
  client: OpenIDClientParts,
  membership: CallMembershipIdentityParts,
  serviceUrl: string,
  forceOldJwtEndpoint: boolean,
  roomId: string,
  delayEndpointBaseUrl?: string,
  delayId?: string,
  logger?: Logger,
): Promise<SFUConfig> {
  let openIdToken: IOpenIDToken;
  try {
    openIdToken = await doNetworkOperationWithRetry(async () =>
      client.getOpenIdToken(),
    );
  } catch (error) {
    throw new FailToGetOpenIdToken(
      error instanceof Error ? error : new Error("Unknown error"),
    );
  }
  logger?.debug("Got openID token", openIdToken);

  logger?.info(`Trying to get JWT for focus ${serviceUrl}...`);

  let sfuConfig: { url: string; jwt: string } | undefined;

  // If forceOldJwtEndpoint is set we indicate that we do not want to try the new endpoint,
  // since we are not sending the new matrix2.0 sticky events (no hashed identity in the event)
  if (forceOldJwtEndpoint === false) {
    try {
      sfuConfig = await getLiveKitJWTWithDelayDelegation(
        membership,
        serviceUrl,
        roomId,
        openIdToken,
        delayEndpointBaseUrl,
        delayId,
      );
      logger?.info(`Got JWT from call's active focus URL.`);
    } catch (e) {
      sfuConfig = undefined;
      logger?.warn(
        `Failed fetching jwt with matrix 2.0 endpoint (retry with legacy)`,
        e,
      );
      logger?.info(`Got JWT from call's active focus URL.`);
    }
  }

  // Either forceOldJwtEndpoint = true or getLiveKitJWTWithDelayDelegation throws -> reset sfuConfig = undefined
  if (sfuConfig === undefined) {
    sfuConfig = await getLiveKitJWT(
      membership.deviceId,
      serviceUrl,
      roomId,
      openIdToken,
    );
  }

  // Pull the details from the JWT
  const [, payloadStr] = sfuConfig.jwt.split(".");
  // TODO: Prefer Uint8Array.fromBase64 when widely available
  const payload = JSON.parse(global.atob(payloadStr)) as SFUJWTPayload;
  return {
    jwt: sfuConfig.jwt,
    url: sfuConfig.url,
    livekitAlias: payload.video.room,
    // NOTE: Currently unused.
    // Probably also not helpful since we now compute the backendIdentity on joining the call so we can use it for the encryption manager.
    // The only reason for us to know it locally is to connect the right users with the lk world. (and to set our own keys)
    livekitIdentity: payload.sub,
  };
}

async function getLiveKitJWT(
  deviceId: string,
  livekitServiceURL: string,
  matrixRoomId: string,
  openIDToken: IOpenIDToken,
): Promise<{ url: string; jwt: string }> {
  try {
    const res = await fetch(livekitServiceURL + "/sfu/get", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        // This is the actual livekit room alias. For the legacy jwt endpoint simply the room id was used.
        room: matrixRoomId,
        openid_token: openIDToken,
        device_id: deviceId,
      }),
    });
    if (!res.ok) {
      throw new Error("SFU Config fetch failed with status code " + res.status);
    }
    return await res.json();
  } catch (e) {
    throw new Error("SFU Config fetch failed with exception", { cause: e });
  }
}

export async function getLiveKitJWTWithDelayDelegation(
  membership: CallMembershipIdentityParts,
  livekitServiceURL: string,
  matrixRoomId: string,
  openIDToken: IOpenIDToken,
  delayEndpointBaseUrl?: string,
  delayId?: string,
): Promise<{ url: string; jwt: string }> {
  const { userId, deviceId, memberId } = membership;

  const body = {
    room_id: matrixRoomId,
    slot_id: "m.call#ROOM",
    openid_token: openIDToken,
    member: {
      id: memberId,
      claimed_user_id: userId,
      claimed_device_id: deviceId,
    },
  };

  let bodyDalayParts = {};
  // Also check for empty string
  if (delayId && delayEndpointBaseUrl) {
    const delayTimeoutMs =
      Config.get().matrix_rtc_session?.delayed_leave_event_delay_ms ?? 1000;
    bodyDalayParts = {
      delay_id: delayId,
      delay_timeout: delayTimeoutMs,
      delay_cs_api_url: delayEndpointBaseUrl,
    };
  }

  try {
    const res = await fetch(livekitServiceURL + "/get_token", {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
      },
      body: JSON.stringify({ ...body, ...bodyDalayParts }),
    });
    if (!res.ok) {
      throw new Error("SFU Config fetch failed with status code " + res.status);
    }
    return await res.json();
  } catch (e) {
    throw new Error("SFU Config fetch failed with exception " + e);
  }
}