To share basic authentication details across multiple APIs, you can use the Basic authentication mechanism within datasources. To do this, click on the + icon next to the datasources section and add an Authenticated API. Enter the Base URL of the API (ex. https://airtable.com) and select the authentication type as Basic.
The username and password can now be configured under the authentication section and will add the base64 version of the username:password to the header of all APIs added under this datasource. Save this datasource and add a new API