The Companies House API requires authentication credentials, in the form of an API key, to be sent with each request.
To obtain an API key, go to Your applications
and register the application with the Companies House Developer Hub as
an API Key application. This will allocate a unique key to the
application which can be sent with any GET request for a public
resource served by the Companies House API.
The Companies House API uses HTTP Basic Authentication to transmit an API key between the client application and the server. Basic authentication is usually made up of a username and password pair; the Companies House API takes the username as the API key and ignores the password, so can be left blank.
For an API key of my_api_key, the following curl request demonstrates
the setting of the Authorization HTTP request header, as defined by
RFC2617.
curl -XGET -u my_api_key: https://api.company-information.service.gov.uk/company/00000006
GET /company/00000006 HTTP/1.1
Host: api.company-information.service.gov.uk
Authorization: Basic bXlfYXBpX2tleTo=
The Companies House API has some functionality that requires OAuth 2.0 authentication for actions that require and end user.
For details on integrating a third party web service with the Companies House OAuth 2.0 service see the guide here and the available API Filing functionality here.