Support custom url schemes for native mobile apps

[kdawgwilk]

As defined in the spec section 7.1 for native mobile app oauth 2.0 an authorization server should support custom url schemes for the mobile app to be able to receive the redirect on. Currently the redirectUrl validation does not support these kinds of custom url schemes.

Example taken from the spec com.example.app:/oauth2redirect/example-provider

I will point out that some platforms like iOS allow you to intercept https domains and still have the app open them also mentioned in the spec section 7.2 and is recommended over the custom url schemes but it is much easier to setup a custom url scheme than to setup support for https link interception through universal links