if (this._authMethod !== 'XOAUTH2' && (!this._auth.credentials || !this._auth.credentials.user || !this._auth.credentials.pass)) {
            if (this._auth.user && this._auth.pass) {
                this._auth.credentials = {
                    user: this._auth.user,
                    pass: this._auth.pass,
                    options: this._auth.options
                };
            } else {
                return callback(this._formatError('Missing credentials for "' + this._authMethod + '"', 'EAUTH', false, 'API'));
            }
        }