/**
 * Sign an outbound HTTP request with HTTP Signatures (draft-cavage-12).
 *
 * @param request - The request to sign (will be cloned, not mutated)
 * @param privateKeyPem - PEM-encoded PKCS8 private key
 * @param keyId - The key ID URI (e.g., "https://domain/users/alice#main-key")
 * @returns A new Request with Signature, Date, and Digest headers added
 */
export declare function signRequest(request: Request, privateKeyPem: string, keyId: string): Promise<Request>;
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