> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mlm-platform.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Link external user to MLM user

> Links an external user ID to an existing MLM user.



## OpenAPI

````yaml api/openapi-integration.yaml post /api/v1/auth/link
openapi: 3.1.0
info:
  title: MLM Platform Integration API
  version: 1.0.0
  description: >
    Tenant integrator APIs for external platform federation and member-data
    access,

    including OIDC token exchange, external user linking, genealogy, referrals,
    and commissions.


    ## Authentication

    All API requests require a tenant API key passed in the `x-tenant-api-key`
    header.


    ## Token Exchange

    External platforms can exchange their JWT tokens for MLM platform tokens
    using

    the `/api/v1/auth/exchange` endpoint.
  contact:
    name: MLM Platform Support
    email: support@mlm-platform.example.com
servers:
  - url: https://app.mlm-platform.com
    description: Production API
  - url: http://localhost:3000
    description: Local Development
security:
  - TenantApiKey: []
tags:
  - name: Auth
    description: Authentication and token exchange
  - name: Genealogy
    description: Member hierarchy and relationships
  - name: Referrals
    description: Referral statistics and QR codes
  - name: Commissions
    description: Commission history and breakdowns
  - name: Webhooks
    description: Webhook receivers for third-party providers (Stripe, Wise)
paths:
  /api/v1/auth/link:
    post:
      tags:
        - Auth
      summary: Link external user to MLM user
      description: Links an external user ID to an existing MLM user.
      operationId: linkExternalUser
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - mlmUserId
                - externalId
                - provider
              properties:
                mlmUserId:
                  type: string
                  format: uuid
                  description: MLM user ID
                externalId:
                  type: string
                  description: External user ID
                provider:
                  type: string
                  description: Provider ID
      responses:
        '200':
          description: User linked successfully
        '400':
          $ref: '#/components/responses/BadRequest'
        '404':
          description: MLM user not found
        '409':
          description: External ID already linked
components:
  responses:
    BadRequest:
      description: Bad request - validation error
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorResponse'
          example:
            error: Validation failed
            code: VALIDATION_ERROR
            details:
              email: Invalid email format
  schemas:
    ErrorResponse:
      type: object
      properties:
        error:
          type: string
        code:
          type: string
        details:
          type: object
  securitySchemes:
    TenantApiKey:
      type: apiKey
      in: header
      name: x-tenant-api-key
      description: Tenant API key for authentication

````