Is there an option of adding auth0 to NativeScript apps?
The answer to the question on the title is no; at this time, there is no officially supported NativeScript SDK. You can check the supported SDK’s at: Product Support Matrix
In relation to the second point, Auth0 provides an authentication and authorization API following OpenID Connect and OAuth2 specifications (among other options, however, these are the most used ones) so it should be possible to integrate with a NativeScript application.
Although I can’t point you to any official documentation or library an online search would suggest that you may at least want to give a look at: GitHub - sitefinitysteve/nativescript-auth0: Nativescript Auth0 https://auth0.com/ social authentication plugin
nativescript-auth0 does not work with new Auth0 libraries now that RO is not available. And the author of GitHub - sitefinitysteve/nativescript-auth0: Nativescript Auth0 https://auth0.com/ social authentication plugin is no longer supporting this plugin. What are my options to use auth0 with nativescript now? I want to use token based authentication and not RO.
nativescript-auth0 does not work with new Auth0 libraries now that RO is not available. And the author of GitHub - sitefinitysteve/nativescript-auth0: Nativescript Auth0 https://auth0.com/ social authentication plugin is no longer supporting this plugin. What are my options to use auth0 with nativescript now? I want to use token based authentication and not RO.
In terms of specific SDK’s as mentioned in the original answer there’s no formal support. If it’s a matter of wanting to use resource owner at /oauth/token instead of /oauth/ro then the API is not that different so you may want to fork the above library or just call the endpoint directly.