App development - guzzle

I’m trying to integrate nextcloud in my current company stack, which handles all authentication through a main server which handles the Oauth2 protocol. Thus, I’m trying to develop an Oauth2 client app, but I’m facing some problems, among them the Guzzle version.

The well known league oauth2 client package requires guzzle version 6 minimum, when nextcloud has version 5.3, which provokes a version conflict and throws an error whenever I try to use the package…

So is there any way to either upgrade guzzle to the latest version in owncloud, or make use of two libraries of different versions in nextcloud ?

Thanks for your help and for this awesome project !