/**
 * Shared auth header builder for Stitch API clients.
 *
 * Both StitchToolClient and StitchProxy call Google APIs that accept either
 * an API key or an OAuth2 Bearer token. This utility centralizes the header
 * logic so both code paths stay in sync.
 */
export interface AuthHeaderOptions {
    apiKey?: string;
    accessToken?: string;
    /** Google Cloud project ID for quota/billing with Bearer auth. */
    quotaProjectId?: string;
}
/**
 * Build auth headers for a Stitch API request.
 *
 * - If `apiKey` is present, sends `X-Goog-Api-Key`.
 * - Otherwise if `accessToken` is present, sends `Authorization: Bearer`
 *   and optionally `X-Goog-User-Project` for quota.
 * - Throws if neither credential is provided.
 */
export declare function buildAuthHeaders(opts: AuthHeaderOptions): Record<string, string>;
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