There are three “basic" Auth types:
Custom
API Key
Basic
Each of these functions in the same way, resting on the Auth Fundamentals.
Custom
Custom Auth does not have or pass any arguments by default. It is functionally a “shell” that you can use to build a custom Auth.
API Key
API Key has a single pre-built argument, which is the API Key credential that will be prompted when using the app in a workflow. It also passes that API key value as x-api-key in the headers of each API call by default. This can be extended with custom arguments passed in any way needed through the API configuration or individual action configuration.
Basic
Basic Authentication is a simple HTTP protocol scheme, sending Base64-encoded username and password in the Authorization header, prefixed with “Basic.”
The default arguments are simply username and password/