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

Many mobile and desktop computing [platforms|Operating Systems] support inter-app communication via [URIs] by allowing [Applications] to register [Private URI Scheme] (sometimes colloquially referred to as "[custom URI scheme]") like "com.example.app".  When the browser or another app attempts to load a [URI] with a [Private URI Scheme], the [Application] that registered it is launched to handle the request.

To perform an [OAuth 2.0] [Authorization Request] with a [{$pagename}], the [Native application] launches the [browser] with a standard [Authorization Request], but one where the redirection URI utilizes a [Private URI Scheme] it registered with the [Operating System].

When choosing a URI scheme to associate with the [app], [apps] [MUST] use a [URI Scheme] based on a [DNS Domain] name under their control, expressed in [Reverse domain name notation], as recommended by Section 3.8 of [RFC 7595] for [Private URI Schemes].

For example, an app that controls the domain name "app.example.com" can use "com.example.app" as their scheme.  Some [Authorization Servers] assign client identifiers based on [DNS Domain] names, for [example],
%%prettify 
{{{
client1234.usercontent.example.net
}}} 
/%
which can also be used as the [DNS Domain] name for the scheme when reversed in the same manner.  

A [URI Scheme] such as "myapp", however, would not meet this requirement, as it is not based on a [DNS Domain] name.

When there are multiple [Applications] by the same publisher, care must be taken so that each [URI Scheme] is [unique|Collision-Resistant Name] within that group. On platforms that use [Application] identifiers ([GUID]) based on [reverse domain name notation], those identifiers can be reused as the [Private URI Scheme] for the [redirect_uri] to help avoid this problem.

Following the requirements of Section 3.2 of [RFC 3986], as there is no naming authority for [{$pagename}], only a single slash ("/") appears after the scheme component.  A complete example of a redirect URI utilizing a [Private URI Scheme] is:
%%prettify 
{{{
com.example.app:/oauth2redirect/example-provider
}}} 
/%
When the [Authorization Server] completes the request, it redirects to the client's redirection URI as it would normally.  As the redirection URI uses a private-use URI scheme, it results in the [Operating System] launching the [native application], passing in the [URI] as a launch [parameter].  Then, the [native application] uses normal processing for the [Authorization Response].

%%warning
[{$pagename}] has no requirement that the [Private URI Scheme] is a [DNS Domain] under the [Application] developer's control. Therefore [Claimed Https Scheme URI Redirection] is [RECOMMENDED]
%%

%%information
[{$pagename}] uses uses URI (ie NOT [HTTP] redirection) and [App-claimed HTTPS URI Redirection|Claimed Https Scheme URI Redirection] uses URL (ie [HTTP] redirection).
%%

The [Custom URI scheme patterns] are supported on the [Operating Systems].

!! 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-7.1|target='_blank'] - based on information obtained 2016-01-15