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When you create a session you tell Kayle which claims you need. The user sees those claims and the reasons you supplied during the consent step, then either consents and continues or aborts. Only the consented claims are returned in the verification.session.succeeded webhook.

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The request shape

{
  "share_fields": {
    "date_of_birth": {
      "required": true,
      "reason": "Check age eligibility for this product"
    },
    "given_names": {
      "required": false,
      "reason": "Personalise your account profile"
    }
  }
}
Each entry is keyed by the claim’s identifier and contains:
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required
boolean
required
When true, the user must consent to share this claim or the Kayle check cannot proceed. When false, the user can decline this claim individually and still finish the flow.
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reason
string
required
Human-readable reason shown to the user during consent. 1 to 200 characters. Write it for the user, not your engineers.
A session can request at most 32 share fields. Unknown claim keys reject with UNKNOWN_CLAIM_KEY.

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Static claims

These are the claim keys Kayle understands by default:
KeySourceWhat it is
document_type_codeMRZ (DG1)ISO 7501-1 document type, e.g. P for passport.
issuing_country_codeMRZ (DG1)Three-letter ICAO state code of the issuer.
family_nameMRZ (DG1)Surname as printed in the MRZ.
given_namesMRZ (DG1)Given names as printed in the MRZ.
document_numberMRZ (DG1)The document’s serial number.
nationality_codeMRZ (DG1)Three-letter ICAO state code for nationality.
date_of_birthMRZ (DG1)ISO 8601 date (YYYY-MM-DD). Centuries are inferred from expiry where the MRZ is ambiguous.
sex_markerMRZ (DG1)M, F, or X.
document_expiry_dateMRZ (DG1)ISO 8601 date.
mrz_optional_dataMRZ (DG1)The optional data field of the MRZ, raw. Most documents leave this blank.
kayle_document_idDerivedStable identifier for this document for this organization. Lets you recognise the same document on a future Kayle check without storing the document number.
kayle_human_idDerivedStable identifier for the human, derived from the cryptographically attested document. Lets you recognise the same person across re-issued documents within your organization.

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Age-over derived claims

You can request age_over_N for any integer N between 12 and 130. The returned value is a boolean computed from date_of_birth. Use these instead of date_of_birth when you only need a threshold check, since the user will see “Age Over 18” in consent rather than “Date of Birth” — less information disclosed. 
{
  "share_fields": {
    "age_over_18": { "required": true, "reason": "Check legal age for our service" }
  }
}

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Defaults

If you create a session without share_fields, Kayle applies a default contract that includes kayle_document_id. The session response normalises everything into share_fields with a source field per entry:
  • source: "rc" — requested by you (the relying client).
  • source: "default" — added by Kayle’s default contract.

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Receiving the values

When Kayle confirms an attempt, the verification.session.succeeded webhook returns the consented claims: 
{
  "type": "verification.session.succeeded",
  "data": {
    "claims": {
      "date_of_birth": "1995-04-12",
      "family_name": "Curie",
      "given_names": "Marie",
      "kayle_document_id": "kdid_..."
    },
    "selected_field_keys": ["date_of_birth", "family_name", "given_names", "kayle_document_id"]
  },
  "metadata": { "verification_session_id": "vs_...", "event_id": "evt_...", "contract_version": 1 }
}
selected_field_keys is the canonical list of keys the user actually consented to share. Optional fields the user declined will be missing from claims even though you requested them — code defensively.