Identity

Use the Identity API to manage user identifiers. With this API, you can programmatically add a client user identifier or custom identifier(s) to a user.
You should only use clientUserId and customIdentifiers to send Attentive your system-assigned unique identifiers (even when testing).

Notes:

• Sending duplicate values could lead to unintentionally bridging users together.
• Don't use customIdentifiers to send attributes (e.g., first name, last name). To send those types of attributes,
  use our Custom Attributes API.
• Avoid sending null values or empty strings. If you don't have a valid identifier, you should omit the field
  from the payload.