Send OTP to signer email

Requires the four session-binding headers (see x-fsig-session-* component parameters). 401 session_signature_required when absent. When the deployment has Cloudflare Turnstile configured (TURNSTILE_SECRET_KEY set), the request must also carry a valid turnstile_token; the browser solves the challenge in the OTP modal before this call. A short per-email cooldown (default 30s) plus 15-minute sliding-window rate limits apply.

post/api/envelopes/{envelope_id}/otp

Request

  • Base URL: https://free-sign.com
  • URL: https://free-sign.com/api/envelopes/{envelope_id}/otp
  • Auth: none declared. Required headers: x-fsig-session-signature, x-fsig-session-nonce, x-fsig-session-timestamp, x-fsig-session-action

Path parameters

envelope_idstring required

Headers

x-fsig-session-signaturestring required

Base64url ECDSA P-256 signature over canonicalJson({action, envelope_id, nonce, timestamp}). Produced by the non-extractable session keypair bound to this envelope at creation. See invariant #11 in CLAUDE.md.

x-fsig-session-noncestring required

Random 32-hex-char nonce, fresh per request.

x-fsig-session-timestampstring date-time required

ISO-8601 UTC timestamp of the request. Accepted within +/-5 minutes of server clock.

x-fsig-session-action'otp.request' | 'otp.verify' | 'sign' | 'seal' | 'platform-seal' | 'finalize' | 'webauthn.register' | 'webauthn.authenticate' required

Action name matching the route. Must equal the action field in the signed canonical payload. The webauthn.* actions gate the browser-only passkey endpoints.

Request body

emailstring email required
turnstile_tokenstring

Cloudflare Turnstile token from the browser challenge. Required when the deployment has TURNSTILE_SECRET_KEY set; omitted otherwise. The @smoke.free-sign.com test channel is exempt.

Response

OTP challenge created.

Changes

No recorded changes to this operation across all 1 revision of this API.