import { type RequestEvent } from '@sveltejs/kit';
import type { Handle } from './types.js';
import type { OptionsByStringPath } from '../utils/paths.js';
type MaybePromise<T> = T | Promise<T>;
export interface ProxyOptions {
    to: string;
    requestHook?: (event: RequestEvent) => MaybePromise<Request>;
    /**
     * @example
     * ```ts
     * tweakResponseHeaders(defaultResponseHeaders) {
     *   defaultResponseHeaders.delete('content-encoding')
     *   defaultResponseHeaders.delete('content-length')
     *   return defaultResponseHeaders
     * }
     * ```
     */
    tweakResponseHeaders?: (defaultResponseHeaders: Headers, options: {
        request: Request;
        proxiedUrl?: string;
    }) => Headers;
}
/**
 * Creates a handler which, for requests matching a given path prefix in the given options, proxies
 * the request to the `to` URL in the corresponding {@link ProxyOptions}. Any path elements after
 * the matching prefix are preserved, e.g. a request to `/from/some/other/path` will be proxied to
 * `to/some/other/path`. The request method, body, and headers are preserved, with the exception of
 * the `Host` header which is set to the proxy target hostname.
 *
 * If a `requestHook` is defined, it is called with the original request event before the returned
 * request is proxied. This allows for modifying the request before it is sent, e.g. to add or
 * remove authentication headers, api keys, etc. If the returned request is to a URL with the same
 * origin as the initial request and a path that also starts with the matched path prefix, that
 * request path is proxied; otherwise, the returned request path is not modified before it is
 * fetched. If the `requestHook` function throws, the request is not proxied and a response
 * corresponding to the thrown object (matching Sveltekit endpoint behavior) is returned to the
 * client instead.
 *
 * If multiple options entries would match a request, the first matching entry is used.
 *
 * For requests matching a path prefix in options that do not have an `Origin` header or that have
 * an `Origin` header not matching the request's origin, a 403 Forbidden response is returned. This
 * prevents use of the proxy by other browser applications, but (IMPORTANT) does not prevent abuse
 * of the proxy by applications that can set the `Origin` header manually to match. To prevent this,
 * you can require user authentication and authorization before allowing proxying, validating an
 * incoming request either in a preceding hook or directly in the `requestHook`.
 */
export declare function handleProxies(options: OptionsByStringPath<ProxyOptions>): Handle;
export {};