Authorization via ulogin in a mobile application (Swift/Kotlin+Bitrix)?

Question

API

Good afternoon.
It is necessary to implement authorization through social networks in mobile applications developed in Swift and Kotlin.
Applications use the site database written in 1C-Bitrix through an API written for these applications.
Authorization on the site is implemented through the delaweb.ulogin Bitrix module (ulogin.auth component).

I am interested in the technical scheme of interaction of the application for authorization through social networks, the ideas are as follows:
1) embed the browser into the application, assemble a separate page with a widget on the site, by clicking on the authorization button (for example, VK) a standard page for requesting access to the profile opens (ulogin redirects to it from this url):
https://ulogin.ru/auth.php?name=vkontakte&window=1...
In the post-processor (redirect_uri), somehow separate the request from the site and from the application (?), issue a user token for further use in the application, etc.
2) use the functionality of the application itself (in earlier versions of android / ios, special modules were implemented to work with ulogin, adapt them to swift / kotlin) - in this case, processing of redirect_uri similar to paragraph 1 will probably be required.
3) Your option.

Which option is the least labor intensive?

PS Rejection of ulogin, the implementation of native authorization / registration / merging profiles for this question is rather useless, because the functionality is essentially identical, leading to the redirect_uri handler.
PSS Information security issues raised earlier on this resource in the answers are solved by refusing CDN ulogin by transferring the script to the site server, please do not mention them in the answers.