This is one of the oldest forms of HTTP authentication.
In the context of an HTTP transaction, basic access authentication is a method for an HTTP user agent (e.g. a web browser) to provide a user name and password when making a request. In basic HTTP authentication, a request contains a header field in the form of Authorization: Basic <credentials>, where credentials is the Base64 encoding of ID and password joined by a single colon :.
See the Confluence API for an example of an API which uses this method of authentication.
See https://en.wikipedia.org/wiki/Basic_access_authentication
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