Basecamp Authorization API

openapi: 3.1.0
info:
  title: Basecamp Authorization API
  description: The Basecamp API is a REST API that provides programmatic access to Basecamp's project management and team communication platform. It enables developers to manage projects, to-do lists, messages, documents, schedules, campfires, uploads, card tables, templates, and team members across Basecamp accounts. The API uses OAuth 2.0 for authentication and returns JSON responses, with all requests scoped to an account ID in the base URL path. Resources include projects, people, to-dos, message boards, documents, card tables, campfires, questionnaires, and webhooks, covering the full breadth of Basecamp's collaboration toolset.
  version: '1.0'
  contact:
    name: Basecamp Developer Support
    url: https://github.com/basecamp/bc3-api
  termsOfService: https://basecamp.com/terms
servers:
- url: https://3.basecampapi.com/{accountId}
  description: Production Server
  variables:
    accountId:
      description: Your Basecamp account ID
      default: '999999999'
security:
- bearerAuth: []
tags:
- name: Authorization
  description: OAuth 2.0 authorization code flow endpoints
paths:
  /authorization:
    get:
      operationId: authorizeUser
      summary: Authorize user
      description: Redirects the user to the Basecamp authorization page where they can grant your application access to their account. After the user approves, Basecamp redirects back to your redirect_uri with an authorization code.
      tags:
      - Authorization
      parameters:
      - name: type
        in: query
        required: true
        description: Must be set to "web_server" for the authorization code flow
        schema:
          type: string
          enum:
          - web_server
      - name: client_id
        in: query
        required: true
        description: Your application's client ID from launchpad.37signals.com
        schema:
          type: string
      - name: redirect_uri
        in: query
        required: true
        description: The URI to redirect to after authorization. Must match a URI registered with your application.
        schema:
          type: string
          format: uri
      responses:
        '302':
          description: Redirect to Basecamp authorization page or back to redirect_uri with code parameter on approval
        '400':
          $ref: '#/components/responses/BadRequest'
components:
  responses:
    BadRequest:
      description: Bad request — missing or invalid parameters
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
  schemas:
    Error:
      type: object
      properties:
        error:
          type: string
          description: Human-readable error message
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: 'OAuth 2.0 Bearer token obtained via the Basecamp authorization code flow at launchpad.37signals.com. Include as "Authorization: Bearer {token}" in all requests.'
externalDocs:
  description: Basecamp API Documentation
  url: https://github.com/basecamp/bc3-api