/**
 * Get the SHA-256 of a given string
 *
 * @param text Text to hash
 * @returns Promise<string>
 */
export declare function digestTextSha256(text: string): Promise<string>;
/**
 *
 * @param key
 * @returns The cache string of a given key or undefined if not found
 */
export declare function getCachedString(key: string): Promise<string | undefined>;
/**
 * Save a string on cache with the given key and ttl
 *
 * @param key To identify the saved string
 * @param content Content string to save
 * @param ttl Number of seconds to keep on cache
 */
export declare function saveCachedString(key: string, content: string, ttl?: number): Promise<void>;
/**
 * Get the script nonce from the Content-Security-Policy header
 * @param cspHeader  The Content-Security-Policy header value
 * @returns     The nonce string or null if not found
 */
export declare function getScriptNonceFromHeader(cspHeader: string | null): string | undefined;