OAuth 2.0 token endpoint to exchange authorization code for access token, request token with client credentials, or refresh an existing token.

• Use Authorization Code grant to obtain access token for a Company to use with the Company API.
• Use Refresh Token grant to obtain a new access token using a refresh token.
• Use Client Credentials grant without a scope to obtain a legacy General API token.
• Approved integrations may request Agency API scopes with Client Credentials for
  machine-to-machine agency access. This requires the integration to hold an approved
  agency API client-credentials privilege at the integration level.