core/auth/kratos/identity.schema.json

{
  "$id": "https://schemas.ory.sh/presets/kratos/quickstart/email-password/identity.schema.json",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "User",
  "type": "object",
  "properties": {
    "traits": {
      "type": "object",
      "properties": {
        "username": {
          "type": "string",
          "format": "username",
          "title": "Username",
          "minLength": 3,
          "ory.sh/kratos": {
            "credentials": {
              "password": {
                "identifier": true
              }
            }
          }
        }
      },
      "additionalProperties": false
    }
  }
}