---
ref: tool:segment/identify-user
name: Identify a user
company: company:segment
workflows: []
access: [api]
tags: [capability:track-product-usage, category:cdp, has:api]
docs: https://www.twilio.com/docs/segment/connections/sources/catalog/libraries/server/http-api#identify
updated: 2026-09-27
---

# Identify a user

Records a user's traits, such as email, name and plan, against their user ID and routes them to the source's destinations.

Send `userId` or `anonymousId` and a `traits` object. Segment recommends
identifying once when the account is created and again only when its traits
change. `SEGMENT_API_KEY` holds the base64 of the source's write key followed
by a colon. The API answers 200 even for an event it drops (only oversized
payloads and invalid JSON return 400), so confirm arrival in the source's
Debugger.

## Set up

Use the first option your agent supports.

### API (official)

- Base URL: https://api.segment.io
- Endpoint: `POST /v1/identify`
- Auth: send the header `Authorization: Basic $SEGMENT_API_KEY`
- Get a key: https://www.twilio.com/docs/segment/connections/find-writekey
- Docs: https://www.twilio.com/docs/segment/connections/sources/catalog/libraries/server/http-api

Before doing anything else, make one read-only call to confirm access.

## Rules

- Ask the user before anything that sends messages, costs money, or changes data.
- Never print API keys.