Security and limits

Authentication

• One-time code by email (Better Auth): expires in 5 minutes, 3 attempts, codes stored hashed, rate-limited sending.
• SSO OIDC per domain. Only platform administrators register a provider, after checking that the organization owns the domain: otherwise a provider could issue emails for a domain that is not its own. Better Auth's registration routes are not exposed.
• 7-day web sessions in HttpOnly cookies. No header alone is enough to impersonate someone.
• VS Code connection via approval in the browser, comparing a code displayed on both sides. The token stays encrypted in VS Code's secret storage; the server keeps only its SHA-256 fingerprint. 30-day sessions, revocable.

Data

Data	Where	Note
Organizations, members, invitations, groups, themes, versions, validation reports, preferences, hashed sessions, SSO providers, activity log	SQLite database (Cloudflare D1)	Published versions immutable (SQL constraint)
Published CSS	Platform storage (Cloudflare R2) or organization storage (S3-compatible, Azure Blob)	Never public: the server returns the CSS after checking rights
Storage credentials	Database, encrypted (AES-GCM)	Never returned; storage addresses HTTPS only
CSS sent to the AI assistant	Claude API (Anthropic)	Only if the organization enables it; embedded images and fonts stripped before sending
Markdown presentations and their images	Nowhere	They stay on users' machines

Theme checks

Every theme goes through the theme validator, the same one in the editor, on the server and in the extension:

• CSS read by a real parser: checks apply to decoded values, so an escape sequence cannot hide a URL;
• no external resources: only images and fonts embedded as base64 data:, whose first bytes match the declared type;
• no SVG, no @import except for themes built into Marp, no </style, no legacy script mechanisms;
• every Core v1 class must have an effect, and the geometry of the control slides is checked in a browser.

There is no size limit as a rule: embedded images make the CSS grow. Only the technical limit of a request (64 MB) remains.

The preview is displayed in an isolated iframe, without scripts or network. On the extension side, the organization, name, version and SHA-256 fingerprint of the CSS are verified before installation, then the validator is applied.

What permissions do not do

• A revocation does not erase copies already downloaded and does not prevent their offline use. Permissions govern distribution.
• Geometry (validator stage 6) is measured by the editor's browser: someone who forged their report could only publish in their own organization. Security (stages 1 to 3) is always checked by the server.

Currently out of scope

Storage or collaborative editing of presentations, remote PDF/PPTX rendering, visual theme editor, automatic embedding of images and fonts (imported CSS must already be self-contained), invitations by link, organization deletion, directory synchronization (SCIM), billing.

Before going to production

Open items, to be handled with the final account and domain: email sender domain, request rate limits, database backups, cleanup of orphaned files (replaced drafts) in storage, review of the Ukrainian and Arabic translations.