In this recent post on Medium.com author Paul Redmond shows how to use Guzzle 6 middleware in a Laravel application instead of the framework's own functionality.

The most significant change between Guzzle 5 and 6 is moving away from the event system I grew so accustomed to in Version 5 to middleware in version 6. Needless to say, it was a big adjustment for me at first and it felt like a downgrade. After my initial grumbling, the upgrade guide explains the reasoning for the change.

[...] I prefer to keep my dependencies as up-to-date as possible so I decided to learn Guzzle 6 and become more familiar with the middleware. The concepts are pretty straightforward and I have a few patterns that I like to use when building out middleware within my Laravel applications.

He then shares some code he's used to generate an authorization header and how to add it into the Laravel application as a service using the "tagged" middleware functionality. Finally he shows it in use making a simple request to the endpoint and showing the response results, including the authorization header.