How do I get API access to the Portal?

Request it through your Centrii representative. Centrii issues a Client Key and Client Secret. Your system exchanges them for a short-lived access token (valid for one hour) and uses it to authorise requests, requesting a fresh token when it expires. The token carries the same permissions and asset scope as the account it was issued for, so an integration only sees what it is authorised to see, exactly as in the Portal.