!!! Overview[1]
[{$pagename}] is defined in [OAuth 2.0 for Native Apps] ([RFC 8252])

Some operating systems allow apps to claim "https" scheme [RFC 7230] [URIs] in the domains they control.  When the [browser] encounters a claimed [URI], instead of the page being loaded in the [browser], the
[native application] is launched with the [URI] supplied as a launch [parameter].

Such [URIs] can be used as [redirect_uris] by [native applications]. They are  indistinguishable to the authorization server from a regular web-based client [redirect_uri].  An example is:
%%prettify 
{{{
https://app.example.com/oauth2redirect/example-provider
}}} 
/%

As the [redirect_uri] alone is not enough to distinguish [OAuth Public Client] [native applications] from [OAuth Confidential Client], it is [REQUIRED] in [RFC 8252] Section 8.4 that the [OAuth 2.0 Client Type] be recorded during [OAuth 2.0 Client Registration] to enable the [Authorization Server] to determine the [OAuth 2.0 Client Type] and act accordingly.

App-claimed "https" scheme redirect URIs have some advantages compared to other native app redirect options in that the identity of the destination app is guaranteed to the [Authorization Server] by the [Operating System].  For this reason, native apps [SHOULD] use them over the other options where possible.

%%information
[{$pagename}] uses [HTTPS] [URL redirection] and [Private-Use URI Scheme Redirection] uses [URI] (ie NOT [URL redirection]).
%%

!! [OAuth 2.0]
Apps on platforms that allow the user to disable this functionality, or lack it altogether __MUST__ fallback to using [custom URI schemes].

The [Authorization Server] __MUST__ allow the [registration|OAuth 2.0 Client Registration] of [HTTPS] [redirect_uri] for [OAuth Client] to support [{$pagename}].

Apps on platforms that allow the user to disable this functionality, or lack it altogether __MUST__ fallback to using [custom URI schemes].

The [Authorization Server] __MUST__ allow the [OAuth 2.0 Client Registration] of [HTTPS] [redirect_uri] for [non-confidential user-agents] to support [{$pagename}].

!! More Information
There might be more information for this subject on one of the following:
[{ReferringPagesPlugin before='*' after='\n' }]
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* [#1] - [OAuth 2.0 for Native Apps|https://tools.ietf.org/html/rfc8252#section-7.2|target='_blank'] - based on information obtained 2016-01-15