next.js/packages/next/src/server/web/get-edge-preview-props.ts

/**
 * In edge runtime, these props directly accessed from environment variables.
 *   - local: env vars will be injected through edge-runtime as runtime env vars
 *   - deployment: env vars will be replaced by edge build pipeline
 */
export function getEdgePreviewProps() {
  return {
    previewModeId: process.env.__NEXT_PREVIEW_MODE_ID || '',
    previewModeSigningKey: process.env.__NEXT_PREVIEW_MODE_SIGNING_KEY || '',
    previewModeEncryptionKey:
      process.env.__NEXT_PREVIEW_MODE_ENCRYPTION_KEY || '',
  }
}