/**
 * AWS Secrets Manager helper for Lambda environments.
 *
 * Fetches secrets via the Lambda Extension which runs on port 2773.
 * The extension caches secrets automatically for performance.
 *
 * @see https://docs.aws.amazon.com/secretsmanager/latest/userguide/retrieving-secrets_lambda.html
 */
/**
 * Fetch a specific field from an AWS Secret stored in Secrets Manager.
 *
 * Uses the Lambda Parameters and Secrets Extension for secure, cached access.
 * The extension expects:
 * - `${envKey}_SECRET_ARN` - The ARN of the secret in Secrets Manager
 * - `${envKey}_SECRET_FIELD` - (Optional) The field name within the JSON secret
 *
 * @param envKey - The environment variable prefix (e.g., 'DATABASE_USERNAME')
 * @returns The secret value, or undefined if not available
 */
export declare function fetchSecretField(envKey: string): Promise<string | undefined>;