/**
 * Interface for a class which can validate nonces to ensure that the same nonce isn't re-used between requests.
 */
export interface NonceValidator {
    /**
     * Checks if the nonce has been used before and saves it if it has not.
     *
     * @param nonce The nonce to check.
     * @param timestamp The timestamp of the message which was included in the signed payload with the nonce.
     *    This can be used to clear out old nonces if desired.
     * @returns true if the nonce was valid and has not been used before, false otherwise.
     */
    checkAndSaveNonce(nonce: string, timestamp: number): Promise<boolean>;
}
/**
 * A simple in-memory nonce validator which caches seen nonce values and rejects any which have been seen before
 * or which are older than a specified limit timestamp. It is not recommended to use this in production, as it will not
 * persist across restarts. You likely want to implement your own validator that persists to a database of some sort.
 */
export declare class InMemoryNonceValidator implements NonceValidator {
    private oldestValidTimestampMs;
    constructor(oldestValidTimestampMs: number);
    private seenNoncesTimestamps;
    checkAndSaveNonce(nonce: string, timestampSec: number): Promise<boolean>;
    /**
     * Purges all nonces older than the given timestamp. This allows the cache to be pruned.
     *
     * @param timestamp A timestamp value in ms before which all nonces should be purged.
     */
    purgeNoncesOlderThan(timestampMs: number): Promise<void>;
}