Verify OTP before browser signing

Returns otp_challenge_id and otp_verified_at so the browser can bind OTP verification into the signed canonical payload. Idempotent: a repeated call with the same signer_id + email + otp_code returns the same verified_at, even after the OTP TTL has elapsed. Idempotency still requires the correct otp_code — signer_id alone is not a bearer token. Fresh (un-verified) calls additionally enforce expires_at and max_attempts. Requires the four session-binding headers (see x-fsig-session-* component parameters).

post/api/envelopes/{envelope_id}/otp/verify

Request

  • Base URL: https://free-sign.com
  • URL: https://free-sign.com/api/envelopes/{envelope_id}/otp/verify
  • 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

signer_idstring required
emailstring email required
otp_codestring required

Response

OTP verified.

signer_idstring required
email_hmacstring required
otp_challenge_idstring required
otp_verified_atstring date-time required

Changes

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