/**
 * Build + sign an S3 presigned-POST policy.
 *
 * @example
 * ```ts
 * const post = signS3PresignedPost({
 *   bucket: 'app-uploads',
 *   region: 'us-east-1',
 *   credentials: { accessKeyId, secretAccessKey },
 *   key: { startsWith: 'avatars/' },
 *   contentType: { startsWith: 'image/' },
 *   contentLengthRange: { min: 0, max: 5 * 1024 * 1024 },
 *   expiresIn: 3600,
 * })
 *
 * // Browser side:
 * //   const fd = new FormData()
 * //   Object.entries(post.fields).forEach(([k, v]) => fd.append(k, v))
 * //   fd.append('file', file)  // MUST be last
 * //   await fetch(post.url, { method: 'POST', body: fd })
 * ```
 */
export declare function signS3PresignedPost(input: S3PresignedPostInput): S3PresignedPostResult;
/**
 * Inputs to {@link signS3PresignedPost}. Mirrors the
 * `presignedUploadPolicy()` adapter call once it's wired up.
 */
export declare interface S3PresignedPostInput {
  bucket: string
  region: string
  credentials: {
    accessKeyId: string
    secretAccessKey: string
    sessionToken?: string
  }
  key: string | { startsWith: string }
  contentType: string | { startsWith: string }
  contentLengthRange?: { min: number, max: number }
  acl?: 'private' | 'public-read' | 'public-read-write' | 'authenticated-read' | 'bucket-owner-read' | 'bucket-owner-full-control'
  expiresIn: number
  fields?: Record<string, string>
}
/**
 * What the browser submits. The form is `multipart/form-data` POSTed
 * to `url`; every key in `fields` becomes a form field with the same
 * name. The actual file MUST be the LAST field, named `'file'`.
 */
export declare interface S3PresignedPostResult {
  url: string
  fields: Record<string, string>
  key: string
}