/// <reference types="node" />
import { EventEmitter } from 'events';
import { GaxiosOptions, GaxiosPromise, GaxiosResponse } from 'gaxios';
import { DefaultTransporter } from '../transporters';
import { Credentials } from './credentials';
import { Headers } from './oauth2client';
/**
 * Defines the root interface for all clients that generate credentials
 * for calling Google APIs. All clients should implement this interface.
 */
export interface CredentialsClient {
    /**
     * The project ID corresponding to the current credentials if available.
     */
    projectId?: string | null;
    /**
     * The expiration threshold in milliseconds before forcing token refresh.
     */
    eagerRefreshThresholdMillis: number;
    /**
     * Whether to force refresh on failure when making an authorization request.
     */
    forceRefreshOnFailure: boolean;
    /**
     * @return A promise that resolves with the current GCP access token
     *   response. If the current credential is expired, a new one is retrieved.
     */
    getAccessToken(): Promise<{
        token?: string | null;
        res?: GaxiosResponse | null;
    }>;
    /**
     * The main authentication interface. It takes an optional url which when
     * present is the endpoint being accessed, and returns a Promise which
     * resolves with authorization header fields.
     *
     * The result has the form:
     * { Authorization: 'Bearer <access_token_value>' }
     * @param url The URI being authorized.
     */
    getRequestHeaders(url?: string): Promise<Headers>;
    /**
     * Provides an alternative Gaxios request implementation with auth credentials
     */
    request<T>(opts: GaxiosOptions): GaxiosPromise<T>;
    /**
     * Sets the auth credentials.
     */
    setCredentials(credentials: Credentials): void;
    /**
     * Subscribes a listener to the tokens event triggered when a token is
     * generated.
     *
     * @param event The tokens event to subscribe to.
     * @param listener The listener that triggers on event trigger.
     * @return The current client instance.
     */
    on(event: 'tokens', listener: (tokens: Credentials) => void): this;
}
export declare interface AuthClient {
    on(event: 'tokens', listener: (tokens: Credentials) => void): this;
}
export declare abstract class AuthClient extends EventEmitter implements CredentialsClient {
    /**
     * The quota project ID. The quota project can be used by client libraries for the billing purpose.
     * See {@link https://cloud.google.com/docs/quota| Working with quotas}
     */
    quotaProjectId?: string;
    transporter: DefaultTransporter;
    credentials: Credentials;
    projectId?: string | null;
    eagerRefreshThresholdMillis: number;
    forceRefreshOnFailure: boolean;
    /**
     * Provides an alternative Gaxios request implementation with auth credentials
     */
    abstract request<T>(opts: GaxiosOptions): GaxiosPromise<T>;
    /**
     * The main authentication interface. It takes an optional url which when
     * present is the endpoint being accessed, and returns a Promise which
     * resolves with authorization header fields.
     *
     * The result has the form:
     * { Authorization: 'Bearer <access_token_value>' }
     * @param url The URI being authorized.
     */
    abstract getRequestHeaders(url?: string): Promise<Headers>;
    /**
     * @return A promise that resolves with the current GCP access token
     *   response. If the current credential is expired, a new one is retrieved.
     */
    abstract getAccessToken(): Promise<{
        token?: string | null;
        res?: GaxiosResponse | null;
    }>;
    /**
     * Sets the auth credentials.
     */
    setCredentials(credentials: Credentials): void;
    /**
     * Append additional headers, e.g., x-goog-user-project, shared across the
     * classes inheriting AuthClient. This method should be used by any method
     * that overrides getRequestMetadataAsync(), which is a shared helper for
     * setting request information in both gRPC and HTTP API calls.
     *
     * @param headers object to append additional headers to.
     */
    protected addSharedMetadataHeaders(headers: Headers): Headers;
}