getAppBetaDecryptionKeys(appID, password, callback) {
		return StdLib.Promises.timeoutCallbackPromise(10000, ['keys'], callback, (resolve, reject) => {
			this._send(EMsg.ClientCheckAppBetaPassword, {
				app_id: appID,
				betapassword: password
			}, (body) => {
				if (body.eresult != EResult.OK) {
					return reject(Helpers.eresultError(body.eresult));
				}

				let branches = {};
				(body.betapasswords || []).forEach((beta) => {
					branches[beta.betaname] = Buffer.from(beta.betapassword, 'hex');
				});

				return resolve({keys: branches});
			});
		});
	}
Request decryption keys for a beta branch of an app from its beta password.
@param {int} appID
@param {string} password
@param {function} [callback] - First arg is Error|null, second is an object mapping branch names to their decryption keys
@return Promise